diff --git a/scons/gallium.py b/scons/gallium.py
index 1a81962..5fc082d 100755
--- a/scons/gallium.py
+++ b/scons/gallium.py
@@ -183,14 +183,15 @@
     # Detect gcc/clang not by executable name, but through pre-defined macros
     # as autoconf does, to avoid drawing wrong conclusions when using tools
     # that overrice CC/CXX like scan-build.
-    env['gcc'] = 0
+    env['gcc_compat'] = 0
     env['clang'] = 0
     env['msvc'] = 0
     if host_platform.system() == 'Windows':
         env['msvc'] = check_cc(env, 'MSVC', 'defined(_MSC_VER)', '/E')
     if not env['msvc']:
-        env['gcc'] = check_cc(env, 'GCC', 'defined(__GNUC__) && !defined(__clang__)')
-        env['clang'] = check_cc(env, 'Clang', '__clang__')
+        env['gcc_compat'] = check_cc(env, 'GCC', 'defined(__GNUC__)')
+    env['clang'] = check_cc(env, 'Clang', '__clang__')
+    env['gcc'] = env['gcc_compat'] and not env['clang']
     env['suncc'] = env['platform'] == 'sunos' and os.path.basename(env['CC']) == 'cc'
     env['icc'] = 'icc' == os.path.basename(env['CC'])
 
@@ -203,7 +204,7 @@
     platform = env['platform']
     x86 = env['machine'] == 'x86'
     ppc = env['machine'] == 'ppc'
-    gcc_compat = env['gcc'] or env['clang']
+    gcc_compat = env['gcc_compat']
     msvc = env['msvc']
     suncc = env['suncc']
     icc = env['icc']
@@ -450,13 +451,13 @@
                 '/O2', # optimize for speed
             ]
         if env['build'] == 'release':
-            ccflags += [
-                '/GL', # enable whole program optimization
-            ]
+            if not env['clang']:
+                ccflags += [
+                    '/GL', # enable whole program optimization
+                ]
         else:
             ccflags += [
                 '/Oy-', # disable frame pointer omission
-                '/GL-', # disable whole program optimization
             ]
         ccflags += [
             '/W3', # warning level
@@ -470,6 +471,10 @@
             '/wd4800', # forcing value to bool 'true' or 'false' (performance warning)
             '/wd4996', # disable deprecated POSIX name warnings
         ]
+        if env['clang']:
+            ccflags += [
+                '-Wno-microsoft-enum-value', # enumerator value is not representable in underlying type 'int'
+            ]
         if env['machine'] == 'x86':
             ccflags += [
                 '/arch:SSE2', # use the SSE2 instructions (default since MSVC 2012)
@@ -556,7 +561,7 @@
             shlinkflags += ['-Wl,--enable-stdcall-fixup']
             #shlinkflags += ['-Wl,--kill-at']
     if msvc:
-        if env['build'] == 'release':
+        if env['build'] == 'release' and not env['clang']:
             # enable Link-time Code Generation
             linkflags += ['/LTCG']
             env.Append(ARFLAGS = ['/LTCG'])