v440.26 - checking kernel headers is broken in conftest.sh

In v440.26, conftest.sh checks if the given kernel headers are available
by trying to compile them. However, it looks for “No such file or directory”
message in the compiler output but it may miss it if a non-English
locale is in use.

As a result, all tested headers are considered present and the kernel
modules fail to compile. Example:

CC [M]  /var/lib/dkms/nvidia-current/440.26-1/build/nvidia/nv-frontend.o
In file included from /var/lib/dkms/nvidia-current/440.26-1/build/nvidia/nv-frontend.c:13:0:
/var/lib/dkms/nvidia-current/440.26-1/build/common/inc/nv-linux.h:131:75: fatal error: asm/system.h: No such file or directory

A simple workaround is to set LC_ALL=C explicitly:

--- a/kernel/conftest.sh
+++ b/kernel/conftest.sh
@@ -70,7 +70,7 @@ translate_and_compile_header_files() {
         CODE="#include <$file>"
         echo "$CODE" > conftest_headers$$.c
-        $CC $CFLAGS -c conftest_headers$$.c > conftest_headers$$.log 2>&1
+        LC_ALL=C $CC $CFLAGS -c conftest_headers$$.c > conftest_headers$$.log 2>&1
         if [ -f conftest_headers$$.o ]; then
             rm -f conftest_headers$$.o