Revert "[APINotes] Prefer diff -u over diff -b"

This reverts commit 3b1ca5e.

This is causing failures on MacOS because the default head
implementation does not support negative numbers. Reverting for now so I
can come up with a more principled fix in the morning.

Author: boomanaiden154

clang/test/APINotes/yaml-roundtrip-2.test

@@ -1,9 +1,11 @@
 RUN: apinotes-test %S/Inputs/Frameworks/SimpleKit.framework/Headers/SimpleKit.apinotes > %t.result
-RUN: not diff -u %S/Inputs/Frameworks/SimpleKit.framework/Headers/SimpleKit.apinotes %t.result | \
-RUN:   tail -n +4 | \
-RUN:   FileCheck %s --implicit-check-not="{{^\+}}" --implicit-check-not="{{^\-}}"
+RUN: not diff -b -e %t.result %S/Inputs/Frameworks/SimpleKit.framework/Headers/SimpleKit.apinotes | FileCheck %s
+
+The `-e` option of `diff` is not implemented in the builtin diff, assume
+that we have a POSIX compatible diff when we have a shell.
+REQUIRES: shell
 
 We expect only the document markers to be emitted
 
-CHECK: +---
-CHECK: +...
+CHECK: 52d
+CHECK: 1d

clang/test/APINotes/yaml-roundtrip.test

@@ -1,18 +1,30 @@
 RUN: apinotes-test %S/Inputs/Frameworks/Simple.framework/Headers/Simple.apinotes > %t.result
-RUN: not diff -u %S/Inputs/Frameworks/Simple.framework/Headers/Simple.apinotes %t.result | \
-RUN:   tail -n +5 | head -n -1 | \
-RUN:   FileCheck %s --implicit-check-not="{{^\+}}" --implicit-check-not="{{^\-}}"
+RUN: not diff -b %S/Inputs/Frameworks/Simple.framework/Headers/Simple.apinotes %t.result | FileCheck %s
+
+Avoid Windows as the diff output differs due to line-endings and different diff
+implementations.
+UNSUPPORTED: system-windows
 
 We expect only the nullability to be different as it is canonicalized during the
 roudtrip.
 
-CHECK:      -        Nullability:     N
-CHECK-NEXT: +        Nullability:     Nonnull
-CHECK:      -        Nullability:     O
-CHECK-NEXT: +        Nullability:     Optional
-CHECK:      -        Nullability:     U
-CHECK-NEXT: +        Nullability:     Unspecified
-CHECK:      -        Nullability:     S
-CHECK-NEXT: +        Nullability:     Unspecified
-CHECK:      -        Nullability:     Scalar
-CHECK-NEXT: +        Nullability:     Unspecified
+CHECK:      7c8
+CHECK-NEXT: <         Nullability:     N
+CHECK-NEXT: ---
+CHECK-NEXT: >         Nullability:     Nonnull
+CHECK-NEXT: 13c14
+CHECK-NEXT: <         Nullability:     O
+CHECK-NEXT: ---
+CHECK-NEXT: >         Nullability:     Optional
+CHECK-NEXT: 19c20
+CHECK-NEXT: <         Nullability:     U
+CHECK-NEXT: ---
+CHECK-NEXT: >         Nullability:     Unspecified
+CHECK-NEXT: 25c26
+CHECK-NEXT: <         Nullability:     S
+CHECK-NEXT: ---
+CHECK-NEXT: >         Nullability:     Unspecified
+CHECK-NEXT: 28c29
+CHECK-NEXT: <         Nullability:     Scalar
+CHECK-NEXT: ---
+CHECK-NEXT: >         Nullability:     Unspecified