gnum4: fix build on loongarch64-linux

pkgs/development/tools/misc/gnum4/default.nix

@@ -14,6 +14,13 @@ stdenv.mkDerivation rec {
     sha256 = "sha256-swapHA/ZO8QoDPwumMt6s5gf91oYe+oyk4EfRSyJqMg=";
   };
 
+  # https://gitweb.gentoo.org/repo/gentoo.git/tree/sys-devel/m4/m4-1.4.19-r1.ebuild
+  patches = lib.optional stdenv.hostPlatform.isLoongArch64 ./loong-fix-build.patch;
+  postPatch = if stdenv.hostPlatform.isLoongArch64 then ''
+    touch ./aclocal.m4 ./lib/config.hin ./configure ./doc/stamp-vti || die
+    find . -name Makefile.in -exec touch {} + || die
+  '' else null;
+
   strictDeps = true;
   enableParallelBuilding = true;
 

pkgs/development/tools/misc/gnum4/loong-fix-build.patch

@@ -0,0 +1,30 @@
+[xen0n: this is https://github.com/sunhaiyong1978/CLFS-for-LoongArch/blob/1.0/patches/stack-direction-add-loongarch.patch with line number tweak, and change to generated file added as well.]
+From: Sun Haiyong <youbest@sina.com>
+Date: Tue, 31 Aug 2021 11:11:52 +0800
+Subject: [PATCH] stack-direction: Add support for loongarch CPU
+
+* m4/stack-direction.m4 (SV_STACK_DIRECTION): When the CPU is loongarch,
+set "sv_cv_stack_direction" to "-1" .
+--- a/m4/stack-direction.m4
++++ b/m4/stack-direction.m4
+@@ -31,6 +31,7 @@ AC_DEFUN([SV_STACK_DIRECTION],
+       i?86 | x86_64 | \
+       i860 | \
+       ia64 | \
++      loongarch* | \
+       m32r | \
+       m68* | \
+       m88k | \
+--- a/configure
++++ b/configure
+@@ -46399,6 +46399,7 @@ else $as_nop
+       i?86 | x86_64 | \
+       i860 | \
+       ia64 | \
++      loongarch* | \
+       m32r | \
+       m68* | \
+       m88k | \
+-- 
+2.17.2
+