libplacebo: fix build on darwin

pkgs/by-name/fa/fast-float/package.nix

@@ -0,0 +1,29 @@
+{ lib
+, stdenv
+, fetchFromGitHub
+, cmake
+}:
+
+stdenv.mkDerivation (finalAttrs: {
+  pname = "fast-float";
+  version = "6.0.0";
+
+  src = fetchFromGitHub {
+    owner = "fastfloat";
+    repo = "fast_float";
+    rev = "v${finalAttrs.version}";
+    hash = "sha256-yKHmturouLJkBAdIWoi8vhmipP6jxAwyA+YoSOl6xPU=";
+  };
+
+  nativeBuildInputs = [
+    cmake
+  ];
+
+  meta = {
+    description = "Fast and exact implementation of the C++ from_chars functions for number types";
+    homepage = "https://github.com/fastfloat/fast_float";
+    license = with lib.licenses; [ asl20 boost mit ];
+    maintainers = with lib.maintainers; [ wegank ];
+    platforms = lib.platforms.all;
+  };
+})

pkgs/development/libraries/libplacebo/default.nix

@@ -14,6 +14,7 @@
 , libunwind
 , libdovi
 , xxHash
+, fast-float
 }:
 
 stdenv.mkDerivation rec {
@@ -46,6 +47,8 @@ stdenv.mkDerivation rec {
     libunwind
     libdovi
     xxHash
+  ] ++ lib.optionals (!stdenv.cc.isGNU) [
+    fast-float
   ];
 
   mesonFlags = with lib; [