cmake: Add compiler warnings for Modern C (C99)

See https://fedoraproject.org/wiki/Changes/PortingToModernC



related: #179

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

CompilerChecks.cmake

@@ -43,6 +43,12 @@ if (UNIX)
     add_c_compiler_flag("-Wno-format-zero-length" SUPPORTED_COMPILER_FLAGS)
     add_c_compiler_flag("-Wmissing-field-initializers" SUPPORTED_COMPILER_FLAGS)
     add_c_compiler_flag("-Wsign-compare" SUPPORTED_COMPILER_FLAGS)
+    add_c_compiler_flag("-Wold-style-definition" SUPPORTED_COMPILER_FLAGS)
+    add_c_compiler_flag("-Werror=old-style-definition" SUPPORTED_COMPILER_FLAGS)
+    add_c_compiler_flag("-Wimplicit-int" SUPPORTED_COMPILER_FLAGS)
+    add_c_compiler_flag("-Werror=implicit-int" SUPPORTED_COMPILER_FLAGS)
+    add_c_compiler_flag("-Wint-conversion" SUPPORTED_COMPILER_FLAGS)
+    add_c_compiler_flag("-Werror=int-conversion" SUPPORTED_COMPILER_FLAGS)
 
     check_c_compiler_flag("-Wformat" REQUIRED_FLAGS_WFORMAT)
     if (REQUIRED_FLAGS_WFORMAT)