[libclang] Fix LibclangReparseTest.FileName when TMPDIR is set to a symlink

Fix testing of clang_File_tryGetRealPathName() in
LibclangReparseTest.FileName when executing in an environment which has
TMPDIR set to a symbolic link that points to an actual directory. The
test would fail because the name returned by
clang_File_tryGetRealPathName() has the symlink resolved but the test
compared it to the original filename of a temporary file.

The patch addresses the problem by checking only that the value returned
by clang_File_tryGetRealPathName() ends with "main.cpp".

Additionally, the patch makes the previous assertion in the test that
checks result of clang_getFileName() stricter. It newly verifies that
the name returned by the function is exactly same as what was given to
clang_parseTranslationUnit()/clang_getFile().

Differential Revision: https://reviews.llvm.org/D45807

llvm-svn: 330507