Driver: Sketch driver support for a CC_LOG_DIAGNOSTICS options, similar to the
existing CC_PRINT_OPTIONS and CC_PRINT_HEADERS, which can be used to
transparently capture the compiler diagnostics from a build.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@129082 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/driver/driver.cpp b/tools/driver/driver.cpp
index 91b48f1..db72da4 100644
--- a/tools/driver/driver.cpp
+++ b/tools/driver/driver.cpp
@@ -423,6 +423,11 @@
   if (TheDriver.CCPrintHeaders)
     TheDriver.CCPrintHeadersFilename = ::getenv("CC_PRINT_HEADERS_FILE");
 
+  // Handle CC_LOG_DIAGNOSTICS and CC_LOG_DIAGNOSTICS_FILE.
+  TheDriver.CCLogDiagnostics = !!::getenv("CC_LOG_DIAGNOSTICS");
+  if (TheDriver.CCLogDiagnostics)
+    TheDriver.CCLogDiagnosticsFilename = ::getenv("CC_LOG_DIAGNOSTICS_FILE");
+
   // Handle QA_OVERRIDE_GCC3_OPTIONS and CCC_ADD_ARGS, used for editing a
   // command line behind the scenes.
   if (const char *OverrideStr = ::getenv("QA_OVERRIDE_GCC3_OPTIONS")) {