Make sure to include config.h in tests/ntpd/nts.c

Otherwise header files are included without our local symbols that control which other symbols are exposed

In this case, the result of trying to build on macOS was:
In file included from ../../tests/ntpd/nts.c:1:
In file included from ../../include/ntpd.h:13:
In file included from ../../include/ntp.h:15:
../../include/ntp_stdlib.h:135:15: error: expected parameter declarator
extern  size_t  strlcpy(char *dst, const char *src, size_t siz);
                ^
/usr/include/secure/_string.h:108:47: note: expanded from macro 'strlcpy'
                __builtin___strlcpy_chk (dest, __VA_ARGS__, __darwin_obsz (dest))
                                                            ^
/usr/include/secure/_common.h:39:62: note: expanded from macro '__darwin_obsz'
                                                             ^
/usr/include/secure/_common.h:30:32: note: expanded from macro '_USE_FORTIFY_LEVEL'
                               ^
In file included from ../../tests/ntpd/nts.c:1:
In file included from ../../include/ntpd.h:13:
In file included from ../../include/ntp.h:15:
../../include/ntp_stdlib.h:135:15: error: expected ')'
/usr/include/secure/_string.h:108:47: note: expanded from macro 'strlcpy'
                __builtin___strlcpy_chk (dest, __VA_ARGS__, __darwin_obsz (dest))
                                                            ^
/usr/include/secure/_common.h:39:62: note: expanded from macro '__darwin_obsz'
                                                             ^
/usr/include/secure/_common.h:30:32: note: expanded from macro '_USE_FORTIFY_LEVEL'
                               ^
../../include/ntp_stdlib.h:135:15: note: to match this '('
/usr/include/secure/_string.h:108:47: note: expanded from macro 'strlcpy'
                __builtin___strlcpy_chk (dest, __VA_ARGS__, __darwin_obsz (dest))
                                                            ^
/usr/include/secure/_common.h:39:53: note: expanded from macro '__darwin_obsz'
                                                    ^
In file included from ../../tests/ntpd/nts.c:1:
In file included from ../../include/ntpd.h:13:
In file included from ../../include/ntp.h:15:
../../include/ntp_stdlib.h:135:15: warning: type specifier missing, defaults to 'int' [-Wimplicit-int]
extern  size_t  strlcpy(char *dst, const char *src, size_t siz);
                ^
/usr/include/secure/_string.h:108:47: note: expanded from macro 'strlcpy'
                __builtin___strlcpy_chk (dest, __VA_ARGS__, __darwin_obsz (dest))
                                                            ^
/usr/include/secure/_common.h:39:31: note: expanded from macro '__darwin_obsz'
                              ^
In file included from ../../tests/ntpd/nts.c:1:
In file included from ../../include/ntpd.h:13:
In file included from ../../include/ntp.h:15:
../../include/ntp_stdlib.h:135:15: error: conflicting types for '__builtin___strlcpy_chk'
/usr/include/secure/_string.h:108:3: note: expanded from macro 'strlcpy'
                __builtin___strlcpy_chk (dest, __VA_ARGS__, __darwin_obsz (dest))
                ^
../../include/ntp_stdlib.h:135:15: note: '__builtin___strlcpy_chk' is a builtin with type 'unsigned long (char *, const char *, unsigned long, unsigned long)'
/usr/include/secure/_string.h:108:3: note: expanded from macro 'strlcpy'
                __builtin___strlcpy_chk (dest, __VA_ARGS__, __darwin_obsz (dest))
                ^
In file included from ../../tests/ntpd/nts.c:1:
In file included from ../../include/ntpd.h:13:
In file included from ../../include/ntp.h:15:
../../include/ntp_stdlib.h:145:15: error: expected parameter declarator
extern  size_t  strlcat(char *dst, const char *src, size_t siz);
                ^
/usr/include/secure/_string.h:115:47: note: expanded from macro 'strlcat'
                __builtin___strlcat_chk (dest, __VA_ARGS__, __darwin_obsz (dest))
                                                            ^
/usr/include/secure/_common.h:39:62: note: expanded from macro '__darwin_obsz'
                                                             ^
/usr/include/secure/_common.h:30:32: note: expanded from macro '_USE_FORTIFY_LEVEL'
                               ^
In file included from ../../tests/ntpd/nts.c:1:
In file included from ../../include/ntpd.h:13:
In file included from ../../include/ntp.h:15:
../../include/ntp_stdlib.h:145:15: error: expected ')'
/usr/include/secure/_string.h:115:47: note: expanded from macro 'strlcat'
                __builtin___strlcat_chk (dest, __VA_ARGS__, __darwin_obsz (dest))
                                                            ^
/usr/include/secure/_common.h:39:62: note: expanded from macro '__darwin_obsz'
                                                             ^
/usr/include/secure/_common.h:30:32: note: expanded from macro '_USE_FORTIFY_LEVEL'
                               ^
../../include/ntp_stdlib.h:145:15: note: to match this '('
/usr/include/secure/_string.h:115:47: note: expanded from macro 'strlcat'
                __builtin___strlcat_chk (dest, __VA_ARGS__, __darwin_obsz (dest))
                                                            ^
/usr/include/secure/_common.h:39:53: note: expanded from macro '__darwin_obsz'
                                                    ^
In file included from ../../tests/ntpd/nts.c:1:
In file included from ../../include/ntpd.h:13:
In file included from ../../include/ntp.h:15:
../../include/ntp_stdlib.h:145:15: warning: type specifier missing, defaults to 'int' [-Wimplicit-int]
extern  size_t  strlcat(char *dst, const char *src, size_t siz);
                ^
/usr/include/secure/_string.h:115:47: note: expanded from macro 'strlcat'
                __builtin___strlcat_chk (dest, __VA_ARGS__, __darwin_obsz (dest))
                                                            ^
/usr/include/secure/_common.h:39:31: note: expanded from macro '__darwin_obsz'
                              ^
In file included from ../../tests/ntpd/nts.c:1:
In file included from ../../include/ntpd.h:13:
In file included from ../../include/ntp.h:15:
../../include/ntp_stdlib.h:145:15: error: conflicting types for '__builtin___strlcat_chk'
/usr/include/secure/_string.h:115:3: note: expanded from macro 'strlcat'
                __builtin___strlcat_chk (dest, __VA_ARGS__, __darwin_obsz (dest))
                ^
../../include/ntp_stdlib.h:145:15: note: '__builtin___strlcat_chk' is a builtin with type 'unsigned long (char *, const char *, unsigned long, unsigned long)'
/usr/include/secure/_string.h:115:3: note: expanded from macro 'strlcat'
                __builtin___strlcat_chk (dest, __VA_ARGS__, __darwin_obsz (dest))
                ^
2 warnings and 6 errors generated.