__loader_cfi_fail: acquire g_dl_mutex

CfiFail calls find_containing_library, which searches the linker's
internal soinfo list, which could be modified by another thread.

Bug: http://b/150372650
Test: bionic-unit-tests
Change-Id: I59024a0a47913caa75702f15ec058b0a360727b5
(cherry picked from commit 172611f5ce)

linker/dlfcn.cpp

@@ -284,6 +284,7 @@ android_namespace_t* __loader_android_get_exported_namespace(const char* name) {
 }
 
 void __loader_cfi_fail(uint64_t CallSiteTypeId, void* Ptr, void *DiagData, void *CallerPc) {
+  ScopedPthreadMutexLocker locker(&g_dl_mutex);
   CFIShadowWriter::CfiFail(CallSiteTypeId, Ptr, DiagData, CallerPc);
 }