[analyzer] Teach scan-build to find clang when installed in /usr/local/bin/

Change scan-build to support the scenario where scan-build is installed in
$TOOLCHAIN/usr/local/bin/ but clang itself is installed in $TOOLCHAIN/usr/bin/.

This is restricted to when 'xcrun' is present; that is, on the Mac.

rdar://problem/48914634

Differential Revision: https://reviews.llvm.org/D59406

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@356308 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit a8c64ce)

Author: devincoughlin

tools/scan-build/bin/scan-build

@@ -1460,6 +1460,16 @@ sub ShellEscape {
   return $arg;
 }
 
+##----------------------------------------------------------------------------##
+# FindXcrun - searches for the 'xcrun' executable. Returns "" if not found.
+##----------------------------------------------------------------------------##
+
+sub FindXcrun {
+  my $xcrun = `which xcrun`;
+  chomp $xcrun;
+  return $xcrun;
+}
+
 ##----------------------------------------------------------------------------##
 # FindClang - searches for 'clang' executable.
 ##----------------------------------------------------------------------------##
@@ -1469,6 +1479,16 @@ sub FindClang {
     $Clang = Cwd::realpath("$RealBin/bin/clang") if (-f "$RealBin/bin/clang");
     if (!defined $Clang || ! -x $Clang) {
       $Clang = Cwd::realpath("$RealBin/clang") if (-f "$RealBin/clang");
+      if (!defined $Clang || ! -x $Clang) {
+        # When an Xcode toolchain is present, look for a clang in the sibling bin
+        # of the parent of the bin directory. So if scan-build is at
+        # $TOOLCHAIN/usr/local/bin/scan-build look for clang at
+        # $TOOLCHAIN/usr/bin/clang.
+        my $has_xcode_toolchain = FindXcrun() ne "";
+        if ($has_xcode_toolchain && -f "$RealBin/../../bin/clang") {
+          $Clang = Cwd::realpath("$RealBin/../../bin/clang");
+        }
+      }
     }
     if (!defined $Clang || ! -x $Clang) {
       return "error: Cannot find an executable 'clang' relative to" .
@@ -1478,8 +1498,7 @@ sub FindClang {
   }
   else {
     if ($Options{AnalyzerDiscoveryMethod} =~ /^[Xx]code$/) {
-      my $xcrun = `which xcrun`;
-      chomp $xcrun;
+      my $xcrun = FindXcrun();
       if ($xcrun eq "") {
         return "Cannot find 'xcrun' to find 'clang' for analysis.\n";
       }