[SCons] Fix warning suppression in external code

ext/SConscript

@@ -5,17 +5,27 @@ localenv = env.Clone()
 
 
 def prep_default(env):
-    return env.Clone()
+    localenv = env.Clone()
+
+    # Suppress warnings from external code and auto-generated code
+    if 'g++' in localenv['CXX']:
+        localenv.Append(CCFLAGS=['-Wno-format', '-Wno-format-security',
+                                 '-Wno-unused-result'])
+
+    if localenv['CC'] == 'clang':
+        localenv['CCFLAGS'].append('-w')
+
+    return localenv
 
 
 def prep_fortran(env):
-    localenv = env.Clone()
+    localenv = prep_default(env)
     localenv.Prepend(CPPPATH='#include/cantera/base')  # for config.h
     return localenv
 
 
 def prep_f2c(env):
-    localenv = env.Clone()
+    localenv = prep_default(env)
 
     localenv.Prepend(CPPPATH=Dir('#ext/f2c_libs'))
     if not localenv['HAS_TIMES_H']:
@@ -26,35 +36,17 @@ def prep_f2c(env):
             print "INFO 2:    prep_f2c: adding MSDOS to CPPDEFINES"
             print "INFO 2:     CPPDEFINES     ", localenv['CPPDEFINES']
 
-    # The F2C code generates a lot of warnings designed to catch
-    # programmer errors, but since this is autogenerated code, those
-    # warnings are irrelevant.
-    if '-Wall' in localenv['CCFLAGS']:
-        localenv['CCFLAGS'].remove('-Wall')
-        localenv['CCFLAGS'].append('-Wno-format-security')
-    elif '/W3' in localenv['CCFLAGS']:
-        localenv['CCFLAGS'].remove('/W3')
-    elif '-Wcheck' in localenv['CCFLAGS']:
-        localenv['CCFLAGS'].remove('-Wcheck')
-    if localenv['CC'] == 'clang':
-        localenv['CCFLAGS'].append('-w')
-
     return localenv
 
 
 def prep_sundials(env):
-    localenv = env.Clone()
+    localenv = prep_default(env)
     localenv.Prepend(CPPPATH=Dir('#ext/cvode/include'))
-
-    # Suppress warnings from external code
-    if '-Wall' in localenv['CCFLAGS']:
-        localenv['CCFLAGS'].append('-Wno-format')
-
     return localenv
 
 
 def prep_gtest(env):
-    localenv = env.Clone()
+    localenv = prep_default(env)
     localenv.Prepend(CPPPATH=[Dir('#ext/gtest'),
                               Dir('#ext/gtest/include')],
                     CPPDEFINES={'GTEST_HAS_PTHREAD': 0})