Print Metal compiler version before running Metal tests

This helps pinpoint the issues due to differences in the Metal compiler
version and also indicates whether we are actually using the compiler to
validate MSL output.

test_shaders.py

@@ -11,6 +11,8 @@ import hashlib
 import shutil
 import argparse
 
+METALC = '/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/usr/bin/metal'
+
 def parse_stats(stats):
     m = re.search('([0-9]+) work registers', stats)
     registers = int(m.group(1)) if m else 0
@@ -62,9 +64,7 @@ def get_shader_stats(shader):
     return parse_stats(returned)
 
 def validate_shader_msl(shader):
-	path = "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/usr/bin/metal"
-	if os.path.exists(path):
-		subprocess.check_call([path, '-x', 'metal', '-std=ios-metal1.0', '-Werror', shader])
+    subprocess.check_call([METALC, '-x', 'metal', '-std=ios-metal1.0', '-Werror', shader])
 
 def cross_compile_msl(shader):
     spirv_f, spirv_path = tempfile.mkstemp()
@@ -76,7 +76,8 @@ def cross_compile_msl(shader):
     subprocess.check_call([spirv_cross_path, '--entry', 'main', '--output', msl_path, spirv_path, '--metal'])
     subprocess.check_call(['spirv-val', spirv_path])
 
-    validate_shader_msl(msl_path)
+    if os.path.exists(METALC):
+        validate_shader_msl(msl_path)
 
     return (spirv_path, msl_path)
 
@@ -279,6 +280,9 @@ def main():
         sys.stderr.write('Need shader folder.\n')
         sys.exit(1)
 
+    if os.path.exists(METALC):
+        subprocess.check_call([METALC, '--version'])
+
     test_shaders(args.folder, args.update, args.malisc, args.keep, 'metal' if args.metal else 'glsl')
     if args.malisc:
         print('Stats in stats.csv!')