Log Message:
PR pkg/48740 - Fix problems on Darwin

Makefile:
  See ${WRKSRC}/libgcc/config/t-slibgcc-darwin: It uses strip(1) to
  create a stub library, not just to remove symbols, so we must not
  let strip(1) be a no-op regardless of ${INSTALL_UNSTRIPPED} or the
  build fails for missing files.

patches/patch-ac:
  Remove the whitespace between $(LINKER_RPATH_FLAG) and the path.
  Otherwise the flag may be misinterpreted by linker (e.g. Apple's ld)

patches/patch-libgcc_config_t-slibgcc-darwin:
  If we don't install libgcc_s.10.[45].dylib, our gcc links binaries
  with *both* /usr/lib/libgcc_s.1.dylib and
  ${GCC_PREFIX}/lib/libgcc_s.1.dylib, which is certainly a bad thing.