Make /fastlink builds as optimized as non-/fastlink builds

build/config/win/BUILD.gn

Index: build/config/win/BUILD.gn
diff --git a/build/config/win/BUILD.gn b/build/config/win/BUILD.gn
index 2b9f7bf77373532e5cca7d033bdd5459d460279f..c36f80cca1754d7571c0fb80d0bf48aa69d76100 100644
--- a/build/config/win/BUILD.gn
+++ b/build/config/win/BUILD.gn
@@ -86,15 +86,32 @@ config("compiler") {
     lib_dirs = [ "$clang_base_path/lib/clang/$clang_version/lib/windows" ]
   }
 
-  # Ensures that the PDB file contains FIXUP information (growing the PDB file
-  # by about 5%) but does not otherwise alter the output binary. This
+  # /PROFILE ensures that the PDB file contains FIXUP information (growing the
+  # PDB file by about 5%) but does not otherwise alter the output binary. This
   # information is used by the Syzygy optimization tool when decomposing the
   # release image. It is enabled for syzyasan builds and opportunistically for
   # other builds where it is not prohibited (not supported when incrementally
   # linking, using /debug:fastlink, or building with clang).
-  if (is_syzyasan ||
-      (!is_debug && !is_component_build && !is_win_fastlink && !is_clang)) {
+  if (is_syzyasan) {
+    assert(!is_win_fastlink)
     ldflags = [ "/PROFILE" ]
+  } else {
+    if (!is_debug && !is_component_build && !is_clang) {
+      if (is_win_fastlink) {
+        # /PROFILE implies the following linker flags. Therefore if we are
+        # skipping /PROFILE because it is incompatible with /DEBUG:FASTLINK
+        # we should explicitly add these flags in order to avoid unintended
+        # consequences such as larger binaries.
+        ldflags = [
+          "/OPT:REF",
+          "/OPT:ICF",
+          "/INCREMENTAL:NO",
+          "/FIXED:NO",
+        ]
+      } else {
+        ldflags = [ "/PROFILE" ]
+      }
+    }
   }
 
   # arflags apply only to static_libraries. The normal linker configs are only