mozjs: apply powerpc build fix patch

Patch is from the firefox recipe in meta-browser, to fix va_list issues with
the powerpc build. This could use a bit further investigation, as the
configure macro is supposed to sort out this define for us.

JIRA: SB-2120

Signed-off-by: Christopher Larson <kergoth@gmail.com>
Merge pull request #108 from kergoth/sb-2120

mozjs: apply powerpc build fix patch