compiler-rt: remove eprintf

It was used by ancient GCC assert.h. Prior to 2001 GCC used to provide
its own assert.h The GCC assert.h required __eprintf to emit the error
message. FreeBSD's own assert.h never used this.

Reviewed by: ed (previously), imp
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D2597