Use a link rather than compile test to for __builtin_bswap64 in libnettle;

fixes little-endian base-gcc (mips64el). From George Koehler, tested by
manphiz@gmail.com, ok aja@.

security/libnettle/Makefile

@@ -1,9 +1,10 @@
-# $OpenBSD: Makefile,v 1.24 2019/06/29 22:26:25 ajacoutot Exp $
+# $OpenBSD: Makefile,v 1.25 2019/12/04 10:36:34 sthen Exp $
 
 COMMENT=		cryptographic library
 
 DISTNAME=		nettle-3.5.1
 PKGNAME=		lib${DISTNAME}
+REVISION=		0
 
 SHARED_LIBS +=  hogweed                   3.0 # 6.5
 SHARED_LIBS +=  nettle                    5.0 # 4.5

security/libnettle/patches/patch-configure

@@ -1,4 +1,7 @@
-$OpenBSD: patch-configure,v 1.8 2019/06/29 22:26:25 ajacoutot Exp $
+$OpenBSD: patch-configure,v 1.9 2019/12/04 10:36:34 sthen Exp $
+
+The test for __builtin_bswap64 must fail if the linker can't find the
+symbol.  We need this for base-gcc on little endian, like mips64el.
 
 Fix relocation errors on (at least) sparc64.
 
@@ -7,6 +10,15 @@ We don't want extra debug flags in regular builds.
 Index: configure
 --- configure.orig
 +++ configure
+@@ -6062,7 +6062,7 @@ uint64_t y = __builtin_bswap64(x);
+   return 0;
+ }
+ _ACEOF
+-if ac_fn_c_try_compile "$LINENO"; then :
++if ac_fn_c_try_link "$LINENO"; then :
+   nettle_cv_c_builtin_bswap64=yes
+ else
+   nettle_cv_c_builtin_bswap64=no
 @@ -6720,6 +6720,7 @@ else
  	bsdi4.*)	CCPIC="-fPIC" ;;
  	bsdi*)		CCPIC="" ;;