Add command line flag --warning-errors and gcc compat alias -Werror

Cython/Compiler/CmdLine.py

@@ -38,6 +38,7 @@ Options:
   -2                             Compile based on Python-2 syntax and code semantics.
   -3                             Compile based on Python-3 syntax and code semantics.
   --fast-fail                    Abort the compilation on the first error
+  --warning-error, -Werror       Make all warnings into errors
   -X, --directive <name>=<value>[,<name=value,...] Overrides a compiler directive
 """
 
@@ -131,6 +132,8 @@ def parse_command_line(args):
                 options.language_level = 3
             elif option == "--fast-fail":
                 Options.fast_fail = True
+            elif option in ('-Werror', '--warning-errors'):
+                Options.warning_errors = True
             elif option == "--disable-function-redefinition":
                 Options.disable_function_redefinition = True
             elif option in ("-X", "--directive"):

Cython/Compiler/Errors.py

@@ -176,6 +176,8 @@ def message(position, message, level=1):
 def warning(position, message, level=0):
     if level < LEVEL:
         return
+    if Options.warning_errors:
+        return error(position, message)
     warn = CompileWarning(position, message)
     line = "warning: %s\n" % warn
     if listing_file:

Cython/Compiler/Options.py

@@ -22,6 +22,9 @@ annotate = False
 # to keep going and printing further error messages.
 fast_fail = False
 
+# Make all warnings into errors.
+warning_errors = False
+
 # This will convert statements of the form "for i in range(...)"
 # to "for i from ..." when i is a cdef'd integer type, and the direction
 # (i.e. sign of step) can be determined.