lp_solve: ignore implicit int warnings, add x64 darwin ldflags

the configuration code generates small c programs with a main function
sans return type specifer. this causes clang builds to fail. add
'-Wno-error=implicit-int' to fix the build.

add -headerpad_max_install_names to env.NIX_LDFLAGS for x64 darwin

pkgs/applications/science/math/lp_solve/default.nix

@@ -22,6 +22,12 @@ stdenv.mkDerivation rec {
     autoSignDarwinBinariesHook
   ];
 
+  env = {
+    NIX_CFLAGS_COMPILE = "-Wno-error=implicit-int";
+  } // lib.optionalAttrs (stdenv.isDarwin && stdenv.isx86_64) {
+    NIX_LDFLAGS = "-headerpad_max_install_names";
+  };
+
   dontConfigure = true;
 
   buildPhase =