[RFC] ppc64le enablement (#45340)

* ppc64le enablement

* gcc, glibc: properly handle __float128

* lib/systems, stdenv: syntax cleanup

* gcc7: remove ugly hack

* gcc: add/update __float128 flags

* stdenv: add another pair of quotes for consistency

* gcc: move __float128 flag for ppc64le-glibc into common/platform-flags.nix

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

@@ -1,4 +1,4 @@
-{ stdenv, lib, fetchurl
+{ stdenv, lib, fetchurl, hostPlatform
 , linuxHeaders ? null
 , useBSDCompatHeaders ? true
 }:
@@ -61,11 +61,12 @@ stdenv.mkDerivation rec {
     configureFlagsArray+=("--syslibdir=$out/lib")
   '';
 
+  CFLAGS="-fstack-protector-strong" + lib.optionalString hostPlatform.isPower " -mlong-double-64";
+
   configureFlags = [
     "--enable-shared"
     "--enable-static"
     "--enable-debug"
-    "CFLAGS=-fstack-protector-strong"
     "--enable-wrapper=all"
   ];