add stackprotector support on musl32

In order to support stackprotector on musl32, this change import a
couple of patches from alpinelinux:
1. libssp_nonshared.a is built alongside musl's libc
2. the above library is automatically linked when compiling with gcc6
   or gcc7

pkgs/development/compilers/gcc/6/default.nix

@@ -78,7 +78,11 @@ let majorVersion = "6";
       ++ optional (targetPlatform.libc == "musl") ../libgomp-dont-force-initial-exec.patch
 
       # Obtain latest patch with ../update-mcfgthread-patches.sh
-      ++ optional (!crossStageStatic && targetPlatform.isMinGW) ./Added-mcf-thread-model-support-from-mcfgthread.patch;
+      ++ optional (!crossStageStatic && targetPlatform.isMinGW) ./Added-mcf-thread-model-support-from-mcfgthread.patch
+      ++ optional (targetPlatform.libc == "musl" && targetPlatform.isx86_32) (fetchpatch {
+        url = "https://git.alpinelinux.org/aports/plain/main/gcc/gcc-6.1-musl-libssp.patch?id=5e4b96e23871ee28ef593b439f8c07ca7c7eb5bb";
+        sha256 = "1jf1ciz4gr49lwyh8knfhw6l5gvfkwzjy90m7qiwkcbsf4a3fqn2";
+      });
 
     javaEcj = fetchurl {
       # The `$(top_srcdir)/ecj.jar' file is automatically picked up at

pkgs/development/compilers/gcc/7/default.nix

@@ -72,6 +72,10 @@ let majorVersion = "7";
       })
       ++ optional langFortran ../gfortran-driving.patch
       ++ optional (targetPlatform.libc == "musl" && targetPlatform.isPower) ../ppc-musl.patch
+      ++ optional (targetPlatform.libc == "musl" && targetPlatform.isx86_32) (fetchpatch {
+        url = "https://git.alpinelinux.org/aports/plain/main/gcc/gcc-6.1-musl-libssp.patch";
+        sha256 = "1jf1ciz4gr49lwyh8knfhw6l5gvfkwzjy90m7qiwkcbsf4a3fqn2";
+      })
       ++ optional (targetPlatform.libc == "musl") ../libgomp-dont-force-initial-exec.patch
 
       # Obtain latest patch with ../update-mcfgthread-patches.sh

pkgs/os-specific/linux/musl/default.nix

@@ -16,6 +16,11 @@ let
     sha256 = "14igk6k00bnpfw660qhswagyhvr0gfqg4q55dxvaaq7ikfkrir71";
   };
 
+  stack_chk_fail_local_c = fetchurl {
+    url = "https://git.alpinelinux.org/aports/plain/main/musl/__stack_chk_fail_local.c?h=3.10-stable";
+    sha256 = "1nhkzzy9pklgjcq2yg89d3l18jif331srd3z3vhy5qwxl1spv6i9";
+  };
+
   # iconv tool, implemented by musl author.
   # Original: http://git.etalabs.net/cgit/noxcuse/plain/src/iconv.c?id=02d288d89683e99fd18fe9f54d4e731a6c474a4f
   # We use copy from Alpine which fixes error messages, see:
@@ -87,6 +92,16 @@ stdenv.mkDerivation rec {
 
   NIX_DONT_SET_RPATH = true;
 
+  preBuild = ''
+    ${if (stdenv.targetPlatform.libc == "musl" && stdenv.targetPlatform.isx86_32) then
+    "# the -x c flag is required since the file extension confuses gcc
+    # that detect the file as a linker script.
+    $CC -x c -c ${stack_chk_fail_local_c} -o __stack_chk_fail_local.o
+    $AR r libssp_nonshared.a __stack_chk_fail_local.o"
+      else ""
+    }
+  '';
+
   postInstall = ''
     # Not sure why, but link in all but scsi directory as that's what uclibc/glibc do.
     # Apparently glibc provides scsi itself?
@@ -96,6 +111,13 @@ stdenv.mkDerivation rec {
     $STRIP -S $out/lib/libc.a
     mkdir -p $out/bin
 
+
+    ${if (stdenv.targetPlatform.libc == "musl" && stdenv.targetPlatform.isx86_32) then
+      "install -D libssp_nonshared.a $out/lib/libssp_nonshared.a
+      $STRIP -S $out/lib/libssp_nonshared.a"
+      else ""
+    }
+
     # Create 'ldd' symlink, builtin
     ln -rs $out/lib/libc.so $out/bin/ldd