acpica-tools: fix cross

The default value of INSTALLFLAGS is "-m 555 -s", -s being the option
to run the "strip" program on the installed files.  When
cross-compiling, we don't have a strip program (we have
"${stdenv.cc.targetPrefix}strip"), so install fails.

The simplest fix for this is to just remove -s from INSTALLFLAGS,
since stdenv will automatically strip all installed binaries at the
end anyway.

pkgs/tools/system/acpica-tools/default.nix

@@ -26,6 +26,9 @@ stdenv.mkDerivation rec {
 
   nativeBuildInputs = [ bison flex ];
 
+  # We can handle stripping ourselves.
+  INSTALLFLAGS = "-m 555";
+
   installFlags = [ "PREFIX=${placeholder "out"}" ];
 
   meta = with lib; {