[ld] add --print-* for diagnostics

This adds the following for passthrough to lld:
- `--print-gc-sections`
- `--print-icf-sections`
- `--print-map`

I am not adding these to the cache manifest, since it does not change
the produced artifacts.

Tested with an example from ziglang#11398: it successfully prints the resulting
map and the GC'd sections.

src/Compilation.zig

@@ -845,6 +845,9 @@ pub const InitOptions = struct {
     linker_shared_memory: bool = false,
     linker_global_base: ?u64 = null,
     linker_export_symbol_names: []const []const u8 = &.{},
+    linker_print_gc_sections: bool = false,
+    linker_print_icf_sections: bool = false,
+    linker_print_map: bool = false,
     each_lib_rpath: ?bool = null,
     build_id: ?bool = null,
     disable_c_depfile: bool = false,
@@ -1694,6 +1697,9 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
             .shared_memory = options.linker_shared_memory,
             .global_base = options.linker_global_base,
             .export_symbol_names = options.linker_export_symbol_names,
+            .print_gc_sections = options.linker_print_gc_sections,
+            .print_icf_sections = options.linker_print_icf_sections,
+            .print_map = options.linker_print_map,
             .z_nodelete = options.linker_z_nodelete,
             .z_notext = options.linker_z_notext,
             .z_defs = options.linker_z_defs,

src/link.zig

@@ -159,6 +159,9 @@ pub const Options = struct {
     version_script: ?[]const u8,
     soname: ?[]const u8,
     llvm_cpu_features: ?[*:0]const u8,
+    print_gc_sections: bool,
+    print_icf_sections: bool,
+    print_map: bool,
 
     objects: []Compilation.LinkObject,
     framework_dirs: []const []const u8,

src/link/Elf.zig

@@ -1475,6 +1475,18 @@ fn linkWithLLD(self: *Elf, comp: *Compilation, prog_node: *std.Progress.Node) !v
             try argv.append("--gc-sections");
         }
 
+        if (self.base.options.print_gc_sections) {
+            try argv.append("--print-gc-sections");
+        }
+
+        if (self.base.options.print_icf_sections) {
+            try argv.append("--print-icf-sections");
+        }
+
+        if (self.base.options.print_map) {
+            try argv.append("--print-map");
+        }
+
         if (self.base.options.eh_frame_hdr) {
             try argv.append("--eh-frame-hdr");
         }

src/main.zig

@@ -656,6 +656,9 @@ fn buildOutputType(
     var linker_max_memory: ?u64 = null;
     var linker_shared_memory: bool = false;
     var linker_global_base: ?u64 = null;
+    var linker_print_gc_sections: bool = false;
+    var linker_print_icf_sections: bool = false;
+    var linker_print_map: bool = false;
     var linker_z_nodelete = false;
     var linker_z_notext = false;
     var linker_z_defs = false;
@@ -1704,6 +1707,12 @@ fn buildOutputType(
                     linker_gc_sections = true;
                 } else if (mem.eql(u8, arg, "--no-gc-sections")) {
                     linker_gc_sections = false;
+                } else if (mem.eql(u8, arg, "--print-gc-sections")) {
+                    linker_print_gc_sections = true;
+                } else if (mem.eql(u8, arg, "--print-icf-sections")) {
+                    linker_print_icf_sections = true;
+                } else if (mem.eql(u8, arg, "--print-map")) {
+                    linker_print_map = true;
                 } else if (mem.eql(u8, arg, "--allow-shlib-undefined") or
                     mem.eql(u8, arg, "-allow-shlib-undefined"))
                 {
@@ -2765,6 +2774,9 @@ fn buildOutputType(
         .linker_initial_memory = linker_initial_memory,
         .linker_max_memory = linker_max_memory,
         .linker_shared_memory = linker_shared_memory,
+        .linker_print_gc_sections = linker_print_gc_sections,
+        .linker_print_icf_sections = linker_print_icf_sections,
+        .linker_print_map = linker_print_map,
         .linker_global_base = linker_global_base,
         .linker_export_symbol_names = linker_export_symbol_names.items,
         .linker_z_nodelete = linker_z_nodelete,