[compiler-rt] Make get_test_cc_for_arch() complain on accidental extra args

[thakis]

Summary

This would've helped find the bug mentioned in 9531fc37fb8b84e4
faster.

[thakis]

Maybe there's a better way to say "this macro should take no varargs"?

[dvyukov]

I don't have cmake readability, but looks reasonable.
Better to merge after the fix for metadata tests.

compiler-rt/cmake/config-ix.cmake

else()
     endif()
   endif()
 endfunction()
 
 # Returns a compiler and CFLAGS that should be used to run tests for the
 # specific architecture.  When cross-compiling, this is controled via
 # COMPILER_RT_TEST_COMPILER and COMPILER_RT_TEST_COMPILER_CFLAGS.
 macro(get_test_cc_for_arch arch cc_out cflags_out)
+  if (NOT ${ARGC} EQUAL 3)
+    message(FATAL_ERROR "got too many args. expected 3, got ${ARGC} (namely: ${ARGV})")
+  endif()
   if(ANDROID OR (NOT APPLE AND ${arch} MATCHES "arm|aarch64|riscv32|riscv64"))
     # This is only true if we are cross-compiling.
     # Build all tests with host compiler and use host tools.
     set(${cc_out} ${COMPILER_RT_TEST_COMPILER})
     set(${cflags_out} ${COMPILER_RT_TEST_COMPILER_CFLAGS})
   else()
     get_target_flags_for_arch(${arch} ${cflags_out})
     if(APPLE)