configure: Fix check_exec_crash for ICL support

Change the check_exec_crash test to use a function pointer instead of
simply calling the function. The EBP availability test will crash when
compiled with ICL likely due to compiler optimization shenanigans.

Originally the check_exec_crash code was moved out of main to fix a
problem with gcc's treatment of non-leaf main on x86_32. Libav already
moved the code out of main but the addition of the function pointer will
prevent any inlining which fixes the remaining problem.

A function pointer is used since it is compiler agnostic (as opposed to
say __attribute__ ((noinline)) which would only work with gcc compatible
compilers).
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

configure

@@ -911,6 +911,7 @@ static void sighandler(int sig){
 int foo(void){
     $code
 }
+int (*func_ptr)(void) = foo;
 int main(void){
     signal(SIGILL, sighandler);
     signal(SIGFPE, sighandler);
@@ -918,7 +919,7 @@ int main(void){
 #ifdef SIGBUS
     signal(SIGBUS, sighandler);
 #endif
-    foo();
+    return func_ptr();
 }
 EOF
 }