Clarify dlfcn.dladdr_libc slightly.

This isn't a very helpful way to say "realpath() failed":
```
bionic/tests/dlfcn_test.cpp:(1006) Failure in test dlfcn.dladdr_libc
Value of: realpath("/system/lib64/" "hwasan/libc.so", libc_realpath) == libc_realpath
  Actual: false
Expected: true
```

Bug: http://b/278795547
Test: treehugger
Change-Id: I1078ab4a675b956327f2578086a1a5e7d8a2928b

1 files changed, 7 insertions, 6 deletions

diff --git a/tests/dlfcn_test.cpp b/tests/dlfcn_test.cpp
index 3f70279c1..f1f7759b4 100644
--- a/tests/dlfcn_test.cpp
+++ b/tests/dlfcn_test.cpp
@@ -981,24 +981,25 @@ TEST(dlfcn, dladdr_libc) {
 #endif
 
   Dl_info info;
-  void* addr = reinterpret_cast<void*>(puts); // well-known libc function
+  void* addr = reinterpret_cast<void*>(puts);  // An arbitrary libc function.
   ASSERT_TRUE(dladdr(addr, &info) != 0);
 
-  char libc_realpath[PATH_MAX];
-
   // Check if libc is in canonical path or in alternate path.
+  const char* expected_path;
   if (strncmp(ALTERNATE_PATH_TO_SYSTEM_LIB,
               info.dli_fname,
               sizeof(ALTERNATE_PATH_TO_SYSTEM_LIB) - 1) == 0) {
     // Platform with emulated architecture.  Symlink on ARC++.
-    ASSERT_TRUE(realpath(ALTERNATE_PATH_TO_LIBC, libc_realpath) == libc_realpath);
+    expected_path = ALTERNATE_PATH_TO_LIBC;
   } else if (strncmp(PATH_TO_BOOTSTRAP_LIBC, info.dli_fname,
                      sizeof(PATH_TO_BOOTSTRAP_LIBC) - 1) == 0) {
-    ASSERT_TRUE(realpath(PATH_TO_BOOTSTRAP_LIBC, libc_realpath) == libc_realpath);
+    expected_path = PATH_TO_BOOTSTRAP_LIBC;
   } else {
     // /system/lib is symlink when this test is executed on host.
-    ASSERT_TRUE(realpath(PATH_TO_LIBC, libc_realpath) == libc_realpath);
+    expected_path = PATH_TO_LIBC;
   }
+  char libc_realpath[PATH_MAX];
+  ASSERT_TRUE(realpath(expected_path, libc_realpath) != nullptr) << strerror(errno);
 
   ASSERT_STREQ(libc_realpath, info.dli_fname);
   // TODO: add check for dfi_fbase