gcc: always inhibit libc in cross with same configs

It's not just gcc->clang cross compilation that produces different
platforms with equal configs — dynamic->static cross compilation can
have the same result (e.g. pkgsMusl.pkgsStatic). So, remove the check
for LLVM, but keep the check that the configs match.

This fixes pkgsMusl.nix on x86_64-linux, which depends on
pkgsMusl.pkgsStatic.buildPackages.gccWithoutTargetLibc.cc.

Fixes: 926c920c1270 ("gcc: tighten condition for inhibit_libc=true")

pkgs/development/compilers/gcc/common/pre-configure.nix

···
 
 # Normally (for host != target case) --without-headers automatically
 # enables 'inhibit_libc=true' in gcc's gcc/configure.ac. But case of
-# gcc->clang "cross"-compilation manages to evade it: there
+# gcc->clang or dynamic->static "cross"-compilation manages to evade it: there
 # hostPlatform != targetPlatform, hostPlatform.config == targetPlatform.config.
 # We explicitly inhibit libc headers use in this case as well.
 + lib.optionalString (targetPlatform != hostPlatform &&
                       withoutTargetLibc &&
-                      targetPlatform.config == hostPlatform.config &&
-                      (stdenv.cc.isClang || stdenv.targetPlatform.useLLVM or false)) ''
+                      targetPlatform.config == hostPlatform.config) ''
   export inhibit_libc=true
 ''