clang: Suppress a -Wstring-conversion warnings in nspr, gyp edition.

nss.gyp

Index: nss.gyp
===================================================================
--- nss.gyp	(revision 293108)
+++ nss.gyp	(working copy)
@@ -253,6 +253,10 @@
               # nspr passes "int*" through "unsigned int*".
               '-Wno-pointer-sign',
             ],
+            'clang_warning_flags_unset': [
+              # nspr uses assert(!"foo") instead of assert(false && "foo").

[wtc, 2014/12/01 19:05:11]

PR_ASSERT(!"foo") can be replaced with PR_NOT_REACHED("foo"). I will fix these
in this way in the NSPR upstream.

PR_NOT_REACHED is defined as
http://mxr.mozilla.org/nspr/ident?i=PR_NOT_REACHED

The definition doesn't use the !"foo" construct.

Are you sure the compiler won't warn about assert(false && "foo")? I will need
to use that construct in one place, where the NSPR file defines its own
assertion macro.

+              '-Wstring-conversion',
+            ],
           },
           'conditions': [
             ['OS=="mac" or OS=="ios"', {