unix: Don't use -Wno-error=cpp or #warning; fix strict alias warning.

For the sake of older versions of gcc (and other compilers), don't use
the #warning CPP directive, nor the -Wno-error=cpp option.

Also, fix a strict alias warning in modffi.c for older compilers, and
add a test for ffi module.

Addresses issue #847.

tests/run-tests

@@ -149,7 +149,7 @@ def main():
         if args.test_dirs is None:
             if pyb is None:
                 # run PC tests
-                test_dirs = ('basics', 'micropython', 'float', 'import', 'io', 'misc', 'unicode')
+                test_dirs = ('basics', 'micropython', 'float', 'import', 'io', 'misc', 'unicode', 'unix')
             else:
                 # run pyboard tests
                 test_dirs = ('basics', 'micropython', 'float', 'pyb', 'pybnative', 'inlineasm')

tests/unix/ffi_float.py

@@ -0,0 +1,21 @@
+# test ffi float support
+
+import ffi
+
+def ffi_open(names):
+    err = None
+    for n in names:
+        try:
+            mod = ffi.open(n)
+            return mod
+        except OSError as e:
+            err = e
+    raise err
+
+libc = ffi_open(('libc.so', 'libc.so.0', 'libc.so.6'))
+
+strtof = libc.func("f", "strtof", "sp")
+print('%.6f' % strtof('1.23', None))
+
+strtod = libc.func("d", "strtod", "sp")
+print('%.6f' % strtod('1.23', None))

tests/unix/ffi_float.py.exp

@@ -0,0 +1,2 @@
+1.230000
+1.230000