[compiler-rt][profile][AIX] pass export list for test with shared library

[daltenty]

Summary

This is a follow up to D118101, that added bexpfull to the test on instrprof-get-filename-merge-mode.c on AIX in order to get the
necessary symbols exported. Unfortunately the extra dependent symbols this exports actually cause segfaults, which is why
this isn't really recommended in the first place, so just use an actual export list.

[stevewan]

get_filename_from_DSO is the only symbol to be exported from the shared obj. LGTM. Thanks.

compiler-rt/test/profile/Posix/instrprof-get-filename-merge-mode.c

 // Test __llvm_profile_get_filename when the on-line merging mode is enabled.
 //
+// RUN: echo get_filename_from_DSO > shr.exp
 // RUN: %clang_pgogen -fPIC -shared %shared_linker_xopts -o %t.dso %p/../Inputs/instrprof-get-filename-dso.c
 // RUN: %clang_pgogen -o %t %s %t.dso
 // RUN: env LLVM_PROFILE_FILE="%t-%m.profraw" %run %t
 
 #include <string.h>
 
 const char *__llvm_profile_get_filename(void);
 extern const char *get_filename_from_DSO(void);
 
 int main(int argc, const char *argv[]) {
   const char *filename1 = __llvm_profile_get_filename();
   const char *filename2 = get_filename_from_DSO();
 
   // Exit with code 1 if the two filenames are the same.
   return strcmp(filename1, filename2) == 0;
 }

compiler-rt/test/profile/Posix/lit.local.cfg.py

 def getRoot(config):
   if not config.parent:
     return config
   return getRoot(config.parent)
 
 root = getRoot(config)
 
 if root.host_os in ['Windows']:
   config.unsupported = True
 
 # AIX usually usually makes use of an explicit export list when linking a shared
-# object, but for the purposes of these tests just export all symbols.
+# object, since the linker doesn't export anything by default.
 if root.host_os in ['AIX']:
-  config.substitutions.append(('%shared_linker_xopts', '-Wl,-bexpfull'))
+  config.substitutions.append(('%shared_linker_xopts', '-Wl,-bE:shr.exp'))
 else:
   config.substitutions.append(('%shared_linker_xopts', ''))