Replace %clang_cc1 with %clang in two tests that need the system

headers.

%clang_cc1 expands to a command line containing -nostdsysteminc, which
turns off the use of the system headers.

Hope this doesn't affect the validity of the tests. We'll probably end
up doing this to all the 3C regression tests as part of #346, but for
now, minimize the number of tests we have to think about.

Author: mattmccutchen-cci

clang/test/3C/allocator.c

@@ -4,7 +4,7 @@
 //
 // RUN: rm -rf %t*
 // RUN: 3c -base-dir=%S %s -- | FileCheck -match-full-lines %s
-// RUN: 3c -base-dir=%S %s -- | %clang_cc1  -fno-builtin -verify -fcheckedc-extension -x c -
+// RUN: 3c -base-dir=%S %s -- | %clang -c -fno-builtin -Xclang -verify -fcheckedc-extension -x c -
 // RUN: 3c -base-dir=%S -output-dir=%t.checked %s --
 // RUN: 3c -base-dir=%t.checked %t.checked/allocator.c -- | diff %t.checked/allocator.c -
 // expected-no-diagnostics

clang/test/3C/ptrtoconstarr.c

@@ -1,8 +1,8 @@
 // RUN: rm -rf %t*
 // RUN: 3c -base-dir=%S -alltypes -addcr %s -- | FileCheck -match-full-lines -check-prefixes="CHECK_ALL","CHECK" %s
 // RUN: 3c -base-dir=%S -addcr %s -- | FileCheck -match-full-lines -check-prefixes="CHECK_NOALL","CHECK" %s
-// RUN: 3c -base-dir=%S --addcr %s -- | %clang_cc1  -fcheckedc-extension -x c -
-// RUN: 3c -base-dir=%S --addcr --alltypes %s -- | %clang_cc1  -fcheckedc-extension -x c -
+// RUN: 3c -base-dir=%S --addcr %s -- | %clang -c -fcheckedc-extension -x c -
+// RUN: 3c -base-dir=%S --addcr --alltypes %s -- | %clang -c -fcheckedc-extension -x c -
 // RUN: 3c -base-dir=%S -alltypes -output-dir=%t.checked %s --
 // RUN: 3c -base-dir=%t.checked -alltypes %t.checked/ptrtoconstarr.c -- | diff %t.checked/ptrtoconstarr.c -