Enables parsing for '-Wl,-rpath,' in pkg-config output, allows better support for NixOS linking.

Author: Felix "xq" Queißner

lib/std/Build/Step/Compile.zig

@@ -693,6 +693,8 @@ const PkgConfigResult = struct {
 /// Run pkg-config for the given library name and parse the output, returning the arguments
 /// that should be passed to zig to link the given library.
 fn runPkgConfig(compile: *Compile, lib_name: []const u8) !PkgConfigResult {
+    const wl_rpath_prefix = "-Wl,-rpath,";
+
     const b = compile.step.owner;
     const pkg_name = match: {
         // First we have to map the library name to pkg config name. Unfortunately,
@@ -783,6 +785,8 @@ fn runPkgConfig(compile: *Compile, lib_name: []const u8) !PkgConfigResult {
             try zig_cflags.appendSlice(&[_][]const u8{ "-D", macro });
         } else if (mem.startsWith(u8, arg, "-D")) {
             try zig_cflags.append(arg);
+        } else if (mem.startsWith(u8, arg, wl_rpath_prefix)) {
+            try zig_cflags.appendSlice(&[_][]const u8{ "-rpath", arg[wl_rpath_prefix.len..] });
         } else if (b.debug_pkg_config) {
             return compile.step.fail("unknown pkg-config flag '{s}'", .{arg});
         }