checkpatch: make git output use LANGUAGE=en_US.utf8

checkpatch: make git output use LANGUAGE=en_US.utf8

git output parsing depends on the language being en_US english.

Make the backtick execution of all `git <foo>` commands set the
LANGUAGE of the process to en_US.utf8 before executing the actual
command using `export LANGUAGE=en_US.utf8; git <foo>`.

Because the command is executed in a child process, the parent
LANGUAGE is unchanged.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Joe Perches <[email protected]>
Reported-by: Sean Christopherson <[email protected]>
Reviewed-by: Sean Christopherson <[email protected]>
Tested-by: Sean Christopherson <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>