Detect Clang availability on Mac based on the SDK, not the OS X version

Since we use the Clang from Xcode's toolchain now, the OS version is
not relevant.

In practice this means we will use clang for Xcode 4.2 and up, which
means it's possible to use clang also on Mac OS 10.6 (Snow Leopard),
where Xcode 4.3 is not available.

Change-Id: I9817e237cdd82d10b93aaaa3c90e35767cdca751
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 18 insertions, 13 deletions

diff --git a/configure b/configure
index 1382fd7704..e4cf0fc273 100755
--- a/configure
+++ b/configure
@@ -2445,20 +2445,25 @@ if [ -z "$PLATFORM" ]; then
     PLATFORM_NOTES=
     case "$UNAME_SYSTEM:$UNAME_RELEASE" in
      Darwin:*)
-         OSX_VERSION=`uname -r | cut -d. -f1`
-         # Select compiler. Use g++ unless we find a usable Clang version
-         PLATFORM=macx-g++
-         if [ "$OSX_VERSION" -ge 12 ]; then
-            # We're on Mountain Lion or above. Use Clang. Don't advertise gcc.
+        # Select compiler. Use g++ unless we find a usable Clang version. Note that
+        # we are checking the "Apple" clang/LLVM version number, not the actual
+        # clang/LLVM version number that the Apple version was based on. We look
+        # for Apple clang version 3.0 or higher, which was branched off LLVM 3.0
+        # from SVN, and first included in Xcode 4.2. Also note that we do not care
+        # about the OS version, since we're not using the clang version that comes
+        # with the system. We use 'xcrun' to check the clang version that's part of
+        # the Xcode installation.
+        if [ "$(xcrun -sdk macosx clang -v 2>&1 | sed -n 's/.*version \([0-9]\).*/\1/p')" -ge 3 ]; then
             PLATFORM=macx-clang
-         elif [ "$OSX_VERSION" -eq 11 ]; then
-             # We're on Lion. Check if we have a supported Clang version
-             if [ "$(clang -v 2>&1 | grep -Po '(?<=version )[\d]')" -ge 3 ]; then
-                     PLATFORM=macx-clang
-                     PLATFORM_NOTES="\n    - Also available for Mac OS X: macx-g++\n"
-             fi
-         fi
-         ;;
+
+            # Advertise g++ as an alternative on Lion and below
+            if [ "$(uname -r | cut -d. -f1)" -le 11 ]; then
+                PLATFORM_NOTES="\n    - Also available for Mac OS X: macx-g++\n"
+            fi
+        else
+            PLATFORM=macx-g++
+        fi
+        ;;
      AIX:*)
         #PLATFORM=aix-g++
         #PLATFORM=aix-g++-64