libexecinfo: fix complie issue
define _GNU_SOURCES to fix compile issue:
execinfo.c:76:5: error: unknown type name 'Dl_info'
| Dl_info info;
| ^~~~~~~
| execinfo.c:83:13: warning: implicit declaration of function 'dladdr' [-Wimplicit-function-declaration]
| if (dladdr(buffer[i], &info) != 0) {
V2: Merged two CFLAGS lines into one.
Signed-off-by: Armin Kuster <akuster808@gmail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>