kexec-tools: Use gccStdenv

openembedded may have a patch for clang but i do not think it is worth
it to use it because using clangStdenv on linux is rare

https://bugs.gentoo.org/732050

`nix build --impure --expr 'with import ./. { config = { replaceStdenv = ({ pkgs }: pkgs.clangStdenv); }; }; kexec-tools'`

pkgs/top-level/all-packages.nix

@@ -9705,7 +9705,17 @@ with pkgs;
 
   kestrel = callPackage ../tools/security/kestrel { };
 
-  kexec-tools = callPackage ../os-specific/linux/kexec-tools { };
+  kexec-tools = callPackage ../os-specific/linux/kexec-tools {
+    # clangStdenv fails with
+    # purgatory/arch/i386/entry32-16.S:23:2: error: unknown directive
+    #  .arch i386
+    #  ^
+    # purgatory/arch/i386/entry32-16.S:115:11: error: unknown token in expression
+    #  ljmp %cs:*(realdest - entry16)
+    #           ^
+    # make: *** [Makefile:128: purgatory/arch/i386/entry32-16.o] Error 1
+    stdenv = gccStdenv;
+  };
 
   keepkey_agent = with python3Packages; toPythonApplication keepkey_agent;