gmp: fix the configure script

The config script as it is now fails on gcc version 14.2.1 20240912 (Red Hat 14.2.1-3) (GCC)
This is because one test did not include string.h before memcpy, and two other tests relied
on implicit function definitions -- in one test definitions are moved before the first use
and the second test is removed wholesale as it relies on undefined behavior and tests some
obscure (and ancient) gcc flavor segfault.

src/gmp/acinclude.m4

@@ -518,6 +518,9 @@ GMP_PROG_CC_WORKS_PART([$1], [gnupro alpha ev6 char spilling],
    values being spilled into floating point registers.  The problem doesn't
    show up all the time, but has occurred enough in GMP for us to reject
    this compiler+flags.  */
+
+#include <string.h>
+
 struct try_t
 {
  char dst[2];
@@ -592,26 +595,13 @@ GMP_PROG_CC_WORKS_PART([$1], [long long reliability test 1],
    Extracted from tests/mpn/t-iord_u.c.  Causes Apple's gcc 3.3 build 1640 and
    1666 to segfault with e.g., -O2 -mpowerpc64.  */
 
-#ifdef __GNUC__
+#ifdef __GNUC_
+h(){}g(){}
 typedef unsigned long long t1;typedef t1*t2;
 __inline__ t1 e(t2 rp,t2 up,int n,t1 v0)
 {t1 c,x,r;int i;if(v0){c=1;for(i=1;i<n;i++){x=up[i];r=x+1;rp[i]=r;}}return c;}
 f(){static const struct{t1 n;t1 src[9];t1 want[9];}d[]={{1,{0},{1}},};t1 got[9];int i;
 for(i=0;i<1;i++){if(e(got,got,9,d[i].n)==0)h();g(i,d[i].src,d[i].n,got,d[i].want,9);if(d[i].n)h();}}
-h(){}g(){}
-#else
-int dummy;
-#endif
-])
-
-GMP_PROG_CC_WORKS_PART([$1], [long long reliability test 2],
-[/* The following provokes an internal compiler error on powerpc-apple-darwin.
-   Extracted from mpz/cfdiv_q_2exp.c.  Causes Apple's gcc 3.3 build 1640 and
-   1666 to get an ICE with -O1 -mpowerpc64.  */
-
-#ifdef __GNUC__
-f(int u){int i;long long x;x=u?~0:0;if(x)for(i=0;i<9;i++);x&=g();if(x)g();}
-g(){}
 #else
 int dummy;
 #endif