Revert "Never implicitly add rpaths for each lib dir, add NixOS libdir to rpath"

This reverts commit d7b73af.

I did not look at this closely enough. This is incorrect; it should not
implicitly add rpaths for every library, and it should not disable the
nice default of each_lib_path when compiling for the native OS.

See #16062 where we are working on a follow-up improvement to this.

Author: andrewrk

lib/std/zig/system/NativePaths.zig

@@ -61,7 +61,6 @@ pub fn detect(arena: Allocator, native_info: NativeTargetInfo) !NativePaths {
             } else if (word.len > 2 and word[0] == '-' and word[1] == 'L') {
                 const lib_path = word[2..];
                 try self.addLibDir(lib_path);
-                try self.addRPath(lib_path);
             } else {
                 try self.addWarningFmt("Unrecognized C flag from NIX_LDFLAGS: {s}", .{word});
                 break;

src/Compilation.zig

@@ -1662,7 +1662,7 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
             .llvm_cpu_features = llvm_cpu_features,
             .skip_linker_dependencies = options.skip_linker_dependencies,
             .parent_compilation_link_libc = options.parent_compilation_link_libc,
-            .each_lib_rpath = options.each_lib_rpath orelse false,
+            .each_lib_rpath = options.each_lib_rpath orelse options.is_native_os,
             .build_id = build_id,
             .cache_mode = cache_mode,
             .disable_lld_caching = options.disable_lld_caching or cache_mode == .whole,