Remove /RTC1 for Windows Debug Builds

SwiftShader requests the optimized flags for debug buidls for
performance. This leads to an incompatible use of /O1 and /RTC1.

BUG=chromium:755195

Change-Id: I53b6f99a67d0b8d5fc5932b677ee278aca300702
Reviewed-on: https://swiftshader-review.googlesource.com/11594
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Robert Liao <robliao@chromium.org>
diff --git a/BUILD.gn b/BUILD.gn
index f6c0699..39f72cb 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -33,9 +33,7 @@
       "NO_SANITIZE_FUNCTION=",
     ]
 
-    if (is_debug) {
-      cflags += [ "/RTC1" ]  # Run-Time Error Checks
-    } else {
+    if (!is_debug) {
       defines += [ "ANGLE_DISABLE_TRACE" ]
     }
   } else {