Use -Wno-pointer-sign

Pointer sign warnings are quite common in FreeBSD code.

builder.py

@@ -164,7 +164,8 @@ def commonFlags():
 
 def commonWarnings():
     return ['-Wall',
-            '-Wno-format']
+            '-Wno-format',
+            '-Wno-pointer-sign']
 
 def commonNoWarnings():
     return ['-w']

libbsd_waf.py

@@ -42,6 +42,7 @@ def build(bld):
     if bld.env.WARNINGS:
         common_flags += ["-Wall"]
         common_flags += ["-Wno-format"]
+        common_flags += ["-Wno-pointer-sign"]
     else:
         common_flags += ["-w"]
     cflags = ['-std=gnu11'] + common_flags