fix build on musl libc

Trying to build liburing on musl yields an error:

make[1]: Entering directory '/work/devel/liburing/src'
     CC setup.ol
     CC queue.ol
     CC syscall.ol
In file included from syscall.c:9:
include/liburing/compat.h:6:2: error: unknown type name 'int64_t'
    6 |  int64_t  tv_sec;
      |  ^~~~~~~
make[1]: *** [Makefile:43: syscall.ol] Error 1
make[1]: Leaving directory '/work/devel/liburing/src'
make: *** [Makefile:12: all] Error 2

Ensure that compat.h includes stdint.h.

Signed-off-by: Milan P. Stanić <mps@arvanta.net>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/configure b/configure
index 30b0a5a..25c4142 100755
--- a/configure
+++ b/configure
@@ -301,6 +301,8 @@
 fi
 if test "$__kernel_timespec" != "yes"; then
 cat >> $compat_h << EOF
+#include <stdint.h>
+
 struct __kernel_timespec {
 	int64_t		tv_sec;
 	long long	tv_nsec;