Improve mini installer and official build GN flags

I went through and did some flag auditing to try to get GN's official build mini_installer target as small as GYP's. It's still 512 bytes too large.

Adds the custom mini_installer flags to the "lib" target as well as the main mini_installer target. This removes some imports around exception handling.

Sync some official build flags: LTCG should go on all optimized targets in official builds, not just "optimize max" ones. Doing this on optimize max has no effect because we only set optimize_max on individual libraries that need to be fast, rather than anything that gets linked.

Convert /OPT:REF to /OPT:ICF. GYP specifies both, but ICF seems to imply REF according to MSDN.

Added some missing release mode flags "/d2Zi+", "/Zc:inline", and "/cgthreads:8", which I found missing from GN.

Removed a dependency on "setup" from mini installer, this is captured by the dependency on ":archive" (which already includes the setup dependency).

Review URL: https://codereview.chromium.org/1329833002

Cr-Original-Commit-Position: refs/heads/master@{#347447}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 7cb45ce734f09f358e62fd982c8fa288673b2ab5

config/compiler/BUILD.gn

@@ -1172,6 +1172,8 @@ if (is_win) {
   common_optimize_on_cflags = [
     "/Ob2",  # Both explicit and auto inlining.
     "/Oy-",  # Disable omitting frame pointers, must be after /O2.
+    "/d2Zi+",  # Improve debugging of optimized code.
+    "/Zc:inline",  # Remove unreferenced COMDAT (faster links).
   ]
   if (!is_asan) {
     common_optimize_on_cflags += [
@@ -1183,7 +1185,17 @@ if (is_win) {
       "/Gw",
     ]
   }
-  common_optimize_on_ldflags = [ "/OPT:REF" ]
+  common_optimize_on_ldflags = [ "/OPT:ICF" ]
+  if (is_official_build) {
+    common_optimize_on_ldflags += [
+      # Link-time code generation.
+      "/LTCG",
+
+      # Set the number of LTCG code-gen threads to eight. The default is four.
+      # This gives a 5-10% link speedup.
+      "/cgthreads:8",
+    ]
+  }
 } else {
   common_optimize_on_cflags = [
     # Don't emit the GCC version ident directives, they just end up in the
@@ -1296,7 +1308,6 @@ config("optimize_max") {
         # value of C4702 for PGO builds is likely very small.
         "/wd4702",
       ]
-      ldflags += [ "/LTCG" ]
     }
   } else {
     cflags = [ "-O2" ] + common_optimize_on_cflags