Add COMPILER_RT_ABI attribute to declarations of builtin functions in unittests

Summary:
This makes their local declarations match their definitions for ARM targets,
where they have a different calling convention.

This really only affects functions that use floating point types (since the
runtime functions use soft-float, and some targets may default to hard-float)
but it seemed good to make it uniform and do the int-only ones too.

Differential Revision: http://reviews.llvm.org/D9062

llvm-svn: 235722
diff --git a/compiler-rt/test/builtins/Unit/mulxc3_test.c b/compiler-rt/test/builtins/Unit/mulxc3_test.c
index 4297c16..e77e94f 100644
--- a/compiler-rt/test/builtins/Unit/mulxc3_test.c
+++ b/compiler-rt/test/builtins/Unit/mulxc3_test.c
@@ -20,7 +20,7 @@
 
 // Returns: the product of a + ib and c + id
 
-long double _Complex
+COMPILER_RT_ABI long double _Complex
 __mulxc3(long double __a, long double __b, long double __c, long double __d);
 
 enum {zero, non_zero, inf, NaN, non_zero_nan};