Linuxbrew: Use safe_system for patchelf

Use patchelf in opt_bin rather than bin to support using patchelf HEAD
Linuxbrew: Only change the loader of executables

Do not change the dynamic loader of shared libraries.
binutils: Add --default-names option for Linux

See Homebrew/homebrew#31814
glibc: Add additional tests
glibc: Fix the test which could incorrectly pass

Look for the string 'Usage' rather than 'ld.so, which passed this case:
Inconsistency detected by ld.so: get-dynamic-info.h: 134: elf_get_dynamic_info:
Assertion `info[15] == ((void *)0)' failed!
Linuxbrew: Do not set rpath for glibc

Closes #126
Linuxbrew: keg_only :provided_by_osx only on Mac

keg_only :provided_by_osx is invalid on other systems.
gettext: Add keg_only :provided_by_osx
readline: Add keg_only :provided_by_osx
glibc: Add keg_only
pcre: Add option --without-check
Merge remote-tracking branch 'linux/master' into master.