main/compiler-rt: Fix compiler-rt install location
Alpine currently installs compiler-rt into the following location. [DESTDIR]/lib/clang/[CLANG_VERSION]
However, Clang expects compiler-rt to be located at a specific location. [DESTDIR]/lib/clang/[CLANG_VERSION]/lib/[OS]
This results in clang on Alpine not being able to use compiler-rt. clang -rtlib=compiler-rt hello.c /usr/bin/ld: cannot find crtbeginS.o: No such file or directory /usr/bin/ld: cannot find /usr/lib/clang/9.0.0/lib/linux/libclang_rt.builtins-x86_64.a: No such file or directory /usr/bin/ld: cannot find /usr/lib/clang/9.0.0/lib/linux/libclang_rt.builtins-x86_64.a: No such file or directory /usr/bin/ld: cannot find crtendS.o: No such file or directory
This change corrects the install location and allows clang to use compiler-rt as a runtime library via -rtlib=compiler-rt.