[clang] Use portable "#!/usr/bin/env bash" shebang for tools and utils.

Reviewed By: JDevlieghere

Differential Revision: https://reviews.llvm.org/D110041

clang/tools/diag-build/diag-build.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # diag-build: a tool showing enabled warnings in a project.
 #

clang/utils/make-ast-dump-check.sh

@@ -1,4 +1,4 @@
-#! /bin/bash
+#!/usr/bin/env bash
 
 # This script is intended as a FileCheck replacement to update the test
 # expectations in a -ast-dump test.