buildtools: fix build for some mktemp

buildtools: fix build for some mktemp

build error:
== Build drivers/net/tap
mktemp: cannot create temp file /tmp/dpdk.auto-config-h.sh.XXX.c:
Invalid argument
.../buildtools/auto-config-h.sh: line 86: : No such file or directory
.../drivers/net/tap/Makefile:55: recipe for target
   'tap_autoconf.h.new' failed

Above error observed on Wind River Linux 8.0

`mktemp` command in that system has a restrictions to have X in
the template at the end and at least six of them.

Complied to mktemp requirements and add -xc flag to compiler to say
`temp` file is a C file

Fixes: ff37ca5d3773 ("devtools: use a common prefix for temporary files")

Reported-by: Shuai Zhu <shuaix.zhu@intel.com>
Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>