Remove -march=westmere from CFLAGS and CXXFLAGS if present since this
old version of GCC (end of life for more than five years) does not yet
support the Intel Westmere architecture. [1]
This avoids breaking users who set a global CPUTYPE to westmere.
While here, backport r469788 from lang/gcc6: [2]
Filter the -mretpoline command-line option, which is understood by recent versions of clang (and used in the context of the Spectre security issues), but not GCC (which uses different options for the same) from CFLAGS and CXXFLAGS. This avoids the build of this port via bootstrap, which is the default and leverages both the system compiler (clang in most cases) plus a just built version GCC, to fail due to the latter not knowing -mretpoline.
PR: 250263 [1], 228205 [2]
Reported by: Patrick McMunn <doctorwhoguy@gmail.com> [1]
Submitted by: rozhuk.im@gmail.com [2]