Fix acinclude.m4 for clang.

Also all other compilers which don't support nested functions in C.

Taken from:
https://svnweb.freebsd.org/ports?view=revision&revision=531220

acinclude.m4

@@ -284,8 +284,6 @@ AC_DEFUN([LSH_GCC_ATTRIBUTES],
 	       lsh_cv_c_attribute,
 [ AC_TRY_COMPILE([
 #include <stdlib.h>
-],
-[
 static void foo(void) __attribute__ ((noreturn));
 
 static void __attribute__ ((noreturn))
@@ -294,6 +292,8 @@ foo(void)
   exit(1);
 }
 ],
+[
+],
 lsh_cv_c_attribute=yes,
 lsh_cv_c_attribute=no)])