Fix bug in GCC's target platform detection under some non-English locales

[gnaggnoyil]

According to GNU gettext's documention, the environment variable LANGUAGE will be considered in priority than LANG when GNU gettext tries to get locale-dependent contents. Therefore, for an environment where LANGUAGE is set to some value other than English(e.g. zh_CN), only specifying LANG to be en_US.UTF-8 is not enough to let GCC output English contents thus TARGETPLATFORM would be unable to be obtained and eventually a build error would occur. This PR is intended to fix this problem.