Switch to clang for nocompile tests and rebaseline existing results.

base/callback_unittest.nc

Index: base/callback_unittest.nc
diff --git a/base/callback_unittest.nc b/base/callback_unittest.nc
index 9bddd1f8367cd7af4fc359455c443df00b5767d5..e7607d98e7d0a4ed86a05ef4981877597874a87a 100644
--- a/base/callback_unittest.nc
+++ b/base/callback_unittest.nc
@@ -12,7 +12,7 @@ class Parent {
 class Child : Parent {
 };
 
-#if defined(NCTEST_EQUALS_REQUIRES_SAMETYPE)  // [r"no matching function for call to 'base::Callback<void\(\)>::Equals\(base::Callback<int\(\)>&\)'"]
+#if defined(NCTEST_EQUALS_REQUIRES_SAMETYPE)  // [r"fatal error: no viable conversion from 'Callback<int \(\)>' to 'const Callback<void \(\)>'"]
 
 // Attempting to call comparison function on two callbacks of different type.
 //
@@ -24,7 +24,7 @@ void WontCompile() {
   c1.Equals(c2);
 }
 
-#elif defined(NCTEST_CONSTRUCTION_FROM_SUBTYPE)  // [r"conversion from 'base::Callback<base::Parent\(\)>' to non-scalar type 'base::Callback<base::Child\(\)>'"]
+#elif defined(NCTEST_CONSTRUCTION_FROM_SUBTYPE)  // [r"fatal error: no viable conversion from 'Callback<base::Parent \(\)>' to 'Callback<base::Child \(\)>'"]
 
 // Construction of Callback<A> from Callback<B> if A is supertype of B.
 //
@@ -35,7 +35,7 @@ void WontCompile() {
   Callback<Child(void)> cb_b = cb_a;
 }
 
-#elif defined(NCTEST_ASSIGNMENT_FROM_SUBTYPE)  // [r"no match for 'operator=' in 'cb_a = cb_b'"]
+#elif defined(NCTEST_ASSIGNMENT_FROM_SUBTYPE)  // [r"fatal error: no viable overloaded '='"]
 
 // Assignment of Callback<A> from Callback<B> if A is supertype of B.
 // See explanation for NCTEST_CONSTRUCTION_FROM_SUBTYPE