Force compilers to use english

Compiling was failing with this:

    libv8/ext/libv8/builder.rb:28:in `make_flags': undefined method `include?' for nil:NilClass (NoMethodError)

when calling on `@compiler.target` because my gcc uses a spanish localization, so `TARGET_REGEXP` wasn't finding anything. This is a simple fix to force gcc to use an english locale.

Sorry about the lack of tests, I couldn't figure out how to test this.

PS: While researching this issue I came across the [-dumpmachine](https://gcc.gnu.org/onlinedocs/gcc-4.3.6/gcc/Debugging-Options.html#index-dumpmachine-769) parameter, which exists in every supported gcc version (and in my machine also works with clang, but somehow I think it's using gcc internally). Maybe using that parameter in the future is more solid than regexing `-v`.

    $ gcc -dumpmachine
    x86_64-unknown-linux-gnu

    $ clang -dumpmachine
    x86_64-unknown-linux-gnu

There is also a `-dumpversion` parameter but it was giving me inconsistencies with clang:

    $ gcc -dumpversion
    4.9.1

    $ gcc -v
    (...)
    gcc version 4.9.1 (GCC)

and

    $ clang -dumpversion
    4.2.1

    $ clang -v
    clang version 3.5.0