Add helper comment for icecc users.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 52a91e30392da630a489f467da72539eb8f1407c..026916b46a39d1355e66a796cb8202cac3778ec3 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -170,6 +170,9 @@
         'use_goma%': 0,

[dshwang, 2014/04/23 15:05:20]

we already have use_goma, so imo it's reasonable to introduce use_icecc because
most non-googler use icecc.

         'gomadir%': '',
 
+        # When using icecc, we cannot use some build flags. e.g. debug fission, -B
+        'use_icecc%': 0,
+
         # The system root for cross-compiles. Default: none.
         'sysroot%': '',
         'chroot_cmd%': '',
@@ -261,6 +264,7 @@
       'enable_hidpi%': '<(enable_hidpi)',
       'android_webview_build%': '<(android_webview_build)',
       'use_goma%': '<(use_goma)',
+      'use_icecc%': '<(use_icecc)',

[Mostyn Bramley-Moore, 2014/04/24 07:36:52]

nitpick: move this down a line, to keep the goma settings together.

[dshwang, 2014/04/24 07:51:37]

yes, I'll fix it.

       'gomadir%': '<(gomadir)',
       'enable_app_list%': '<(enable_app_list)',
       'use_default_render_theme%': '<(use_default_render_theme)',
@@ -727,7 +731,7 @@
         # are using a custom toolchain and need to control -B in ldflags.
         # Gold is not used for 32-bit linux builds as it runs out of address
         # space.
-        ['OS=="linux" and (target_arch=="x64" or target_arch=="arm")', {
+        ['OS=="linux" and (target_arch=="x64" or target_arch=="arm") and use_icecc==0', {

[dshwang, 2014/04/24 04:18:57]

use_icecc already set other build flags here.

If we want to change it to following pattern,
['use_icecc==1', {
  'linux_use_bundled_gold%': 0,
  'linux_use_bundled_binutils%': 0,
}],
these definition should stay more upper level, and linux_use_bundled_gold
variable will be in trouble, because "'linux_use_bundled_gold%': 1" means that
define linux_use_bundled_gold as 1 if linux_use_bundled_gold is not defined.
In this case, linux_use_bundled_gold may or may not be defined according to
use_icecc.

So imho current code is more succinct.

[Mostyn Bramley-Moore, 2014/04/24 07:36:52]

Is this really needed?  linux_use_bundled_gold is only used to modify ldflags,
which is only used in link commands, which icecc doesn't distribute anyway.

[dshwang, 2014/04/24 07:51:37]

That's good point. My machine works well without linux_use_bundled_gold.

However, linux_use_bundled_binutils=0 and linux_use_bundled_gold=1 looks
inconsistent to my eyes, because linux_use_bundled_binutils=0 makes gcc use
system "as" or "objcopy" but linux_use_bundled_gold=1 makes ninja use bundled
"ld".
For example, if system binutils version is 2.22, doesn't it break anything?
because we use 2.22 objcopy with 2.24 ld.

[Lei Zhang, 2014/04/24 19:06:42]

I don't think it'll break anything. Before third_party/binutils, we only had
third_party/gold, so we were using the system toolchain for everything but the
linker, which got version bumps independent of everything else.

           'linux_use_bundled_gold%': 1,
         }, {
           'linux_use_bundled_gold%': 0,
@@ -738,7 +742,7 @@
         # be used except on x86 and x86-64 (the only two architectures which
         # are currently checke in).  Force this off via GYP_DEFINES when you
         # are using a custom toolchain and need to control -B in cflags.
-        ['OS=="linux" and (target_arch=="x64")', {
+        ['OS=="linux" and (target_arch=="x64") and use_icecc==0', {
           'linux_use_bundled_binutils%': 1,
         }, {
           'linux_use_bundled_binutils%': 0,
@@ -1043,6 +1047,7 @@
     'v8_optimized_debug%': '<(v8_optimized_debug)',
     'proprietary_codecs%': '<(proprietary_codecs)',
     'use_goma%': '<(use_goma)',
+    'use_icecc%': '<(use_icecc)',

[Mostyn Bramley-Moore, 2014/04/24 07:36:52]

nitpick: move this down a line, to keep the goma settings together.

     'gomadir%': '<(gomadir)',
 
     # Use system protobuf instead of bundled one.
@@ -3204,7 +3209,7 @@
               }],
               # http://gcc.gnu.org/wiki/DebugFission
               # Requires gold and gcc >= 4.8 or clang.
-              ['linux_use_gold_flags==1 and (clang==1 or gcc_version>=48) and binutils_version>=223', {
+              ['linux_use_gold_flags==1 and (clang==1 or gcc_version>=48) and binutils_version>=223 and use_icecc==0', {

[dshwang, 2014/04/24 04:18:57]

There is not foo variable for "if (use_icc) {  foo = 1; }"
icecc can use system gold.

[Mostyn Bramley-Moore, 2014/04/24 07:36:52]

IMO (but I think Nico disagreed previously), this is where we should use a new
linux_use_split_dwarf variable (the "foo" in Lei Zhang's suggestion?).

[dshwang, 2014/04/24 07:51:37]

if we introduce linux_use_split_dwarf, that code looks like
['linux_use_gold_flags==1 and (clang==1 or gcc_version>=48) and
binutils_version>=223 and use_icecc==0', {
'linux_use_split_dwarf': 1
}],
...
['linux_use_split_dwarf==1', {
'cflags': ['-gsplit-dwarf'],
'ldflags': ['-Wl,--gdb-index'],
}],

IMO, looks not very advanced.

When Nico disagreed, icecc needs only binutils_version=0 hack, but now icecc
needs this whole CL. So Nico@, could I ask your opinion?

                 'cflags': ['-gsplit-dwarf'],
                 'ldflags': ['-Wl,--gdb-index'],
               }],