Switch to clang by default on Mac; drop burden of supporting GCC 4.2

Also get rid of that annoying message about -pthread in clang.

makepanda/makepanda.py

@@ -1686,11 +1686,7 @@ def CompileLink(dll, obj, opts):
                 if 'NOARCH:' + arch.upper() not in opts:
                     cmd += " -arch %s" % arch
 
-        if "SYSROOT" in SDK:
-            cmd += " --sysroot=%s -no-canonical-prefixes" % (SDK["SYSROOT"])
-
-        # Android-specific flags.
-        if GetTarget() == 'android':
+        elif GetTarget() == 'android':
             cmd += " -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now"
             if GetTargetArch() == 'armv7a':
                 cmd += " -march=armv7-a -Wl,--fix-cortex-a8"
@@ -1698,6 +1694,9 @@ def CompileLink(dll, obj, opts):
         else:
             cmd += " -pthread"
 
+        if "SYSROOT" in SDK:
+            cmd += " --sysroot=%s -no-canonical-prefixes" % (SDK["SYSROOT"])
+
         if LDFLAGS != "":
             cmd += " " + LDFLAGS
 

makepanda/makepandacore.py

@@ -396,10 +396,16 @@ def CrossCompiling():
     return GetTarget() != GetHost()
 
 def GetCC():
-    return os.environ.get('CC', TOOLCHAIN_PREFIX + 'gcc')
+    if TARGET == 'darwin':
+        return os.environ.get('CC', TOOLCHAIN_PREFIX + 'clang')
+    else:
+        return os.environ.get('CC', TOOLCHAIN_PREFIX + 'gcc')
 
 def GetCXX():
-    return os.environ.get('CXX', TOOLCHAIN_PREFIX + 'g++')
+    if TARGET == 'darwin':
+        return os.environ.get('CXX', TOOLCHAIN_PREFIX + 'clang++')
+    else:
+        return os.environ.get('CXX', TOOLCHAIN_PREFIX + 'g++')
 
 def GetStrip():
     # Hack