Fixed attempt to link against libm with MSVC

SConstruct

@@ -485,8 +485,10 @@ env['FORTRANMODDIR'] = '${TARGET.dir}'
 
 if env['CC'] == 'gcc':
     env['WIN32'] = False
+    env['LIBM'] = ['m']
 elif env['CC'] == 'cl':
     env['WIN32'] = True
+    env['LIBM'] = []
 else:
     assert False
 

ext/SConscript

@@ -21,7 +21,7 @@ if env['build_with_f2c']:
         # TODO: make link flag more general
         arithenv.Append(CPPFLAGS='-DNO_FPINIT')
         arithenv.Program('f2c_libs/arithchk/arithchk', source='f2c_libs/arithchk/arithchk.c',
-                         LIBS=['m'])
+                         LIBS=env['LIBM'])
         arithenv.Command('#ext/f2c_libs/arith.h', 'f2c_libs/arithchk/arithchk$PROGSUFFIX',
                          '$SOURCE > $TARGET')