v4.29.6: fixes for issues #166 to #172

c73e8eb sign extend narrow character constants where char is signed (#166)
7ed4dcb accept several designated initializers for one union member (#167)
a54a6be take the array size of a tentative definition when an initializer completes a redeclaration (#168)
8f5693b accept a declaration directly after a label (#169)
839f448 support __has_include_next (#170)
838974c translate the llvm-mingw (clang 23) x86 intrinsic headers (#171)
55d6473 continue initialization after a nested designator at the designated level (#172)