devel/py-intbitset: Patch out march/mtune/-O3 (Respect CFLAGS)

ports r476958 added BROKEN to non-x86 ARCH's due to:

fails to compile: the clang compiler does not support -march=core2

Ports must respect user CFLAGS, and beside this port appending its own flags,
overriding system/ports supplied CFLAGS, was also adding march/mtune flags,
the former of which was set to an x86 specific CPU.

This change patches out these flags to address the issue.

While I'm here, level up port compliance (strip shared libraries)

Approved by: portmgr (blanket, framework compliance)
MFH: 2018Q3