bpo-30104: Use -fno-strict-aliasing on clang (#1376)

Python/dtoa.c is not compiled correctly with clang 4.0 and
optimization level -O2 or higher, because of an aliasing issue on the
double/ULong[2] union. Only compile dtoa.c with -fno-strict-aliasing.

LLVM bug report:
https://bugs.llvm.org//show_bug.cgi?id=31928
3 files changed