Allow the libc++ build/source paths to contain symlinks.

The filesystem tests were expecting the paths to the build/source directories
did not contain any symlinks. This patch resolves those symlinks before running
the test suite.

llvm-svn: 273323
diff --git a/libcxx/test/support/filesystem_test_helper.hpp b/libcxx/test/support/filesystem_test_helper.hpp
index 7e3c739..7150f79 100644
--- a/libcxx/test/support/filesystem_test_helper.hpp
+++ b/libcxx/test/support/filesystem_test_helper.hpp
@@ -20,6 +20,7 @@
 namespace StaticEnv {
 
 inline fs::path makePath(fs::path const& p) {
+    // env_path is expected not to contain symlinks.
     static const fs::path env_path = LIBCXX_FILESYSTEM_STATIC_TEST_ROOT;
     return env_path / p;
 }
@@ -236,6 +237,7 @@
     }
 
     static bool checkDynamicTestRoot() {
+        // LIBCXX_FILESYSTEM_DYNAMIC_TEST_ROOT is expected not to contain symlinks.
         char* fs_root = std::getenv("LIBCXX_FILESYSTEM_DYNAMIC_TEST_ROOT");
         if (!fs_root) {
             std::printf("ERROR: LIBCXX_FILESYSTEM_DYNAMIC_TEST_ROOT must be a defined "