Bug fix, CPATH="" does not add '.' to search path.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@57072 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Driver/InitHeaderSearch.cpp

@@ -81,7 +81,7 @@ void InitHeaderSearch::AddPath(const std::string &Path, IncludeDirGroup Group,
 
 void InitHeaderSearch::AddEnvVarPaths(const char *Name) {
   const char* at = getenv(Name);
-  if (!at)
+  if (!at || *at == 0) // Empty string should not add '.' path.
     return;
 
   const char* delim = strchr(at, llvm::sys::PathSeparator);

test/Driver/env-include-paths.c

@@ -3,7 +3,6 @@
 // RUN: env CPATH="xyz:xyz" clang -fsyntax-only -verify -DAS_SOURCE %s &&
 // RUN: env CPATH="xyz::xyz" clang -fsyntax-only -verify -DSHOULD_FIND -DAS_SOURCE %s &&
 // RUN: env CPATH="../Driver" clang -fsyntax-only -verify -DSHOULD_FIND -DAS_SOURCE %s
-// XFAIL
 
 #ifdef AS_SOURCE
 #undef AS_SOURCE