Add -fdirect-access-external-data

[Fangrui Song]

Hi, I filed https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98112 which
proposes -fdirect-access-external-data to address some x86-64
GCC/binutils pain[1] and also benefit non-x86 architectures (also see [1]
it can prevent copy relocations).

[1] Mentioned in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98112#c2

Since I am going to add this option to Clang and I hope (once GCC decides to
implement this option the two compilers can use the same option name), I bring
it to your attention.

Please CC me on replies:)