apply -flto and -ffunction-sections when compiling libc++

Author: xxxbxxx

src/libcxx.zig

@@ -174,6 +174,8 @@ pub fn buildLibCXX(comp: *Compilation) !void {
         .want_tsan = comp.bin_file.options.tsan,
         .want_pic = comp.bin_file.options.pic,
         .want_pie = comp.bin_file.options.pie,
+        .want_lto = comp.bin_file.options.lto,
+        .function_sections = comp.bin_file.options.function_sections,
         .emit_h = null,
         .strip = comp.compilerRtStrip(),
         .is_native_os = comp.bin_file.options.is_native_os,
@@ -292,6 +294,8 @@ pub fn buildLibCXXABI(comp: *Compilation) !void {
         .want_tsan = comp.bin_file.options.tsan,
         .want_pic = comp.bin_file.options.pic,
         .want_pie = comp.bin_file.options.pie,
+        .want_lto = comp.bin_file.options.lto,
+        .function_sections = comp.bin_file.options.function_sections,
         .emit_h = null,
         .strip = comp.compilerRtStrip(),
         .is_native_os = comp.bin_file.options.is_native_os,

src/libunwind.zig

@@ -113,6 +113,8 @@ pub fn buildStaticLib(comp: *Compilation) !void {
         .want_tsan = false,
         .want_pic = comp.bin_file.options.pic,
         .want_pie = comp.bin_file.options.pie,
+        .want_lto = comp.bin_file.options.lto,
+        .function_sections = comp.bin_file.options.function_sections,
         .emit_h = null,
         .strip = comp.compilerRtStrip(),
         .is_native_os = comp.bin_file.options.is_native_os,