Instead of using a custom target to copy the startup object file to a
file with the desired name, a normal object library with a special
property is used.
Follow up patches will do more cleanup wrt how the startup objects are
used in integration tests.
Reviewed By: jhuber6
Differential Revision: https://reviews.llvm.org/D143464
We currently put everything in one single archive libc.a which breaks in
certain situations where the compiler drivers expect libm.a also. With
this change, we separate out libc.a and libm.a functions as is done
conventionally and put them in two different static archives.
One will now have to build two targets, `libc` and `libm` which produce
`libc.a` and `libm.a` respectively. Under default build, one still builds only
one target named `libc` which produces `libllvmlibc.a`.
Reviewed By: jhuber6
Differential Revision: https://reviews.llvm.org/D143005
