[UBSan] Fix shared library linking in test for Darwin.

[usama54321]

Summary

Use ld_flags_rpath* substitutions.

Without rpath information, the test fails on some Darwin platforms since the binary fails to find the shared library.

rdar://110010041

[rsundahl]

Thank you for this one @usama54321. LGTM. I was able to look up the Radar but for others, I suggest a sentence in the description of the diff that explains why it was a problem for us.

compiler-rt/test/ubsan/TestCases/TypeCheck/Function/function.cpp

-// RUN: %clangxx -std=c++17 -fsanitize=function %s -O3 -g -DSHARED_LIB -fPIC -shared -o %t-so.so
-// RUN: %clangxx -std=c++17 -fsanitize=function %s -O3 -g -o %t %t-so.so
+// RUN: %clangxx -std=c++17 -fsanitize=function %s -O3 -g -DSHARED_LIB -fPIC -shared -o %dynamiclib %ld_flags_rpath_so
+// RUN: %clangxx -std=c++17 -fsanitize=function %s -O3 -g -o %t %ld_flags_rpath_exe
 // RUN: %run %t 2>&1 | FileCheck %s --check-prefix=CHECK
 // Verify that we can disable symbolization if needed:
 // RUN: %env_ubsan_opts=symbolize=0 %run %t 2>&1 | FileCheck %s --check-prefix=NOSYM
 
 struct Shared {};
 using FnShared = void (*)(Shared *);
 FnShared getShared();