The issue is uncovered by #47698: for IR files without a target triple,
-mtriple= specifies the full target triple while -march= merely sets the
architecture part of the default target triple, leaving a target triple which
may not make sense, e.g. riscv64-apple-darwin.
Therefore, -march= is error-prone and not recommended for tests without a target
triple. The issue has been benign as we recognize $unknown-apple-darwin as ELF instead
of rejecting it outrightly.
Emit references to '__do_global_ctors' and '__do_global_dtors' to allow
constructor/destructor routines to run.
Reviewed by: MaskRay
Differential Revision: https://reviews.llvm.org/D107133
