Revert "compiler-rt: use __GLIBC_PREREQ for SANITIZER_INTERCEPT_GETRANDOM"

Revert "compiler-rt: move all __GLIBC_PREREQ into own header file"

"move all __GLIBC_PREREQ" breaks build on some bots

This reverts commit 2d75ee93.
This reverts commit 7a6461fc.

llvm-svn: 373367