WAF: Fix detection of linker features

WAF: Fix detection of linker features

Following check of linker feature failed with strict CFLAGS
"-Werrorr=implicit-function-declaration -Werror=implicit-int"

  Checking for rpath library support       : not found
  Checking for -Wl,--version-script support  : not found

../main.c: In function ‘main’:
../main.c:1:26: error: implicit declaration of function ‘lib_func’
    [-Werror=implicit-function-declaration]
 int main(void) {return !(lib_func() == 42);}
                          ^~~~~~~~

Signed-off-by: Lukas Slebodnik <lslebodn@redhat.com>
Reviewed-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>