Rework default GN symbol handling for win goma builds.

Win goma builds do not support PDB files, so trying to build with
full symbols is very painful. Previously we would default to "full
symbols" but silently turn off symbols if using goma; this CL
restructures things so that we default to "minimal symbols" if
using goma (and visual studio's compiler).

R=brucedawson@chromium.org, brettw@chromium.org, thakis@chromium.org
BUG=634184

Review-Url: https://codereview.chromium.org/2215433002
Cr-Commit-Position: refs/heads/master@{#415325}

build/config/compiler/BUILD.gn

@@ -1503,14 +1503,8 @@ config("default_optimization") {
 config("symbols") {
   if (is_win) {
     import("//build/toolchain/goma.gni")
-    if (use_goma) {
-      # Disable symbols during goma compilation because otherwise the redundant
-      # debug information (repeated in every .obj file) makes linker memory
-      # consumption and link times unsustainable (crbug.com/630074).
-      cflags = []
-    } else {
-      cflags = [ "/Zi" ]  # Produce PDB file, no edit and continue.
-    }
+    cflags = [ "/Zi" ]  # Produce PDB file, no edit and continue.
+
     if (is_win_fastlink && visual_studio_version != "2013") {
       # Tell VS 2015+ to create a PDB that references debug
       # information in .obj and .lib files instead of copying

build/config/compiler/compiler.gni

@@ -82,6 +82,13 @@ if (symbol_level == -1) {
     # With instrumentation enabled, debug info puts libchrome.so over 4gb, which
     # causes the linker to produce an invalid ELF. http://crbug.com/574476
     symbol_level = 0
+  } else if (is_win && use_goma && !is_clang) {
+    # goma doesn't support PDB files, so we disable symbols during goma
+    # compilation because otherwise the redundant debug information generated
+    # by visual studio (repeated in every .obj file) makes linker
+    # memory consumption and link times unsustainable (crbug.com/630074).
+    # Clang on windows does not have this issue.
+    symbol_level = 1
   } else if (!is_linux || is_debug || is_official_build || is_chromecast) {
     # Linux is slowed by having symbols as part of the target binary, whereas
     # Mac and Windows have them separate, so in Release Linux, default them off,