Migrate the difftypes* tests to the diagnostic verifier.

This feels a little cleaner than manually scanning the stderr and lets
us check the diagnostics more precisely, for what that's worth. We
couldn't do this before #488 both because 3C exited before the
diagnostics could be verified and because 3C didn't support custom
verify prefixes. #488 solved the first problem, and this PR solves the
second.

Author: mattmccutchen-cci

clang/test/3C/difftypes1a.c

@@ -1,7 +1,11 @@
-//RUN: rm -rf %t*
-//RUN: not 3c -base-dir=%S -output-dir=%t.checked %s %S/difftypes1b.c -- 2>%t.stderr
-//RUN: grep -q "merging failed" %t.stderr
+// Since the RUN commands in difftypes1a.c and difftypes1b.c process the two
+// files in different orders and the location where the error is reported
+// depends on the order, we need to use a different diagnostic verification
+// prefix (and set of corresponding comments) for each RUN command.
 
-// The desired behavior in this case is to fail, so other checks are omitted
+//RUN: rm -rf %t*
+//RUN: 3c -base-dir=%S -output-dir=%t.checked %s %S/difftypes1b.c -- -Xclang -verify=ab-expected
 
+// ab-expected-no-diagnostics
+// ba-expected-error@+1 {{merging failed for 'foo'}}
 _Ptr<int> foo(int, char);

clang/test/3C/difftypes1b.c

@@ -1,7 +1,11 @@
-//RUN: rm -rf %t*
-//RUN: not 3c -base-dir=%S -output-dir=%t.checked %s %S/difftypes1a.c -- 2>%t.stderr
-//RUN: grep -q "merging failed" %t.stderr
+// Since the RUN commands in difftypes1a.c and difftypes1b.c process the two
+// files in different orders and the location where the error is reported
+// depends on the order, we need to use a different diagnostic verification
+// prefix (and set of corresponding comments) for each RUN command.
 
-// The desired behavior in this case is to fail, so other checks are omitted
+//RUN: rm -rf %t*
+//RUN: 3c -base-dir=%S -output-dir=%t.checked %s %S/difftypes1a.c -- -Xclang -verify=ba-expected
 
+// ba-expected-no-diagnostics
+// ab-expected-error@+1 {{merging failed for 'foo'}}
 int *foo(int, char *);

clang/test/3C/difftypes2a.c

@@ -1,9 +1,15 @@
+// Since the RUN commands in difftypes2a.c and difftypes2b.c process the two
+// files in different orders and the location where the error is reported
+// depends on the order, we need to use a different diagnostic verification
+// prefix (and set of corresponding comments) for each RUN command.
+
 // RUN: rm -rf %t*
-// RUN: not 3c -base-dir=%S -output-dir=%t.checked %s %S/difftypes2b.c -- 2>%t.stderr
-// RUN: grep -q "merging failed" %t.stderr
+// RUN: 3c -base-dir=%S -output-dir=%t.checked %s %S/difftypes2b.c -- -Xclang -verify=ab-expected
 
 // The desired behavior in this case is to fail, so other checks are omitted
 
 // Test no body vs body
 
+// ab-expected-no-diagnostics
+// ba-expected-error@+1 {{merging failed for 'foo'}}
 void foo(char *x);

clang/test/3C/difftypes2b.c

@@ -1,11 +1,15 @@
-// RUN: rm -rf %t*
-// RUN: not 3c -base-dir=%S -output-dir=%t.checked %s %S/difftypes2a.c -- 2>%t.stderr
-// RUN: grep -q "merging failed" %t.stderr
+// Since the RUN commands in difftypes2a.c and difftypes2b.c process the two
+// files in different orders and the location where the error is reported
+// depends on the order, we need to use a different diagnostic verification
+// prefix (and set of corresponding comments) for each RUN command.
 
-// The desired behavior in this case is to fail, so other checks are omitted
+// RUN: rm -rf %t*
+// RUN: 3c -base-dir=%S -output-dir=%t.checked %s %S/difftypes2a.c -- -Xclang -verify=ba-expected
 
 // Test body vs no body
 
+// ba-expected-no-diagnostics
+// ab-expected-error@+1 {{merging failed for 'foo'}}
 void foo(char **y) {
   // this is the body
 }