Remove unnecessary clang flags for ICU

Remove unnecessary clang flags for ICU

1. -Wno-return-type-c-linkage
 - became unnecessary with ICU bug 9504 fixed 3 years ago.
 - remove from both BUILD.gn and icu.gyp

2. -Wnoheader-hygine
 - became unnecessary a long time ago.
 - remove from BUILD.gn (icu.gyp does not have it)

3. -Wstring-conversion and -Wheader-hygine
 - add to BUILD.gn by NOT excluding clang:extra_warnings

BUG=114660
TEST=Build icuuc/icui18n targets (both gyp and GN) after regenerating build files.
R=brettw@chromium.org, thakis@chromium.org

Committed: https://chromium.googlesource.com/chromium/deps/icu/+/dbed54da22de6f31a38b67672efc5e3db31feb0e

[jungshik at Google, 2015-05-28 00:07:26]

jshin@chromium.org changed reviewers:
+ brettw@chromium.org, thakis@chromium.org

[jungshik at Google, 2015-05-28 00:07:58]

PTAL. Thanks

[Nico, 2015-05-28 02:33:52]

lgtm if it builds

https://codereview.chromium.org/1158933005/diff/1/BUILD.gn
File BUILD.gn (left):

https://codereview.chromium.org/1158933005/diff/1/BUILD.gn#oldcode297
BUILD.gn:297: configs -= [ "//build/config/clang:extra_warnings" ]
I'm not sure if this is right. The comment refers to -Wno-header-hygiene below;
the comment is in the wrong place.

But if ICU builds without disabling extra_warnings, I suppose that's a Good
Thing :-)

https://codereview.chromium.org/1158933005/diff/1/icu.gyp
File icu.gyp (right):

https://codereview.chromium.org/1158933005/diff/1/icu.gyp#newcode200
icu.gyp:200: '-Wno-tautological-compare',
Since the .gn file doesn't have it, you might be able to remove
-Wno-logical-op-parentheses and -Wno-tautological-compare from this target as
well?

[jungshik at Google, 2015-05-28 18:07:13]

Thanks, Nico.

https://codereview.chromium.org/1158933005/diff/1/BUILD.gn
File BUILD.gn (left):

https://codereview.chromium.org/1158933005/diff/1/BUILD.gn#oldcode297
BUILD.gn:297: configs -= [ "//build/config/clang:extra_warnings" ]
On 2015/05/28 02:33:51, Nico wrote:
> I'm not sure if this is right. The comment refers to -Wno-header-hygiene
below;
> the comment is in the wrong place.

builds/config/clang/BUILD.gn has the following (I guess that's the only place
where extra_warnings is defined). |extra_warnings| has '-Wheader-hygiene' and
'-Wstring-conversion'. So, the comment placement makes sense (although one has
to go look at what |extra_warnings| has to understand the comment ;-) ). 

config("extra_warnings") {
  cflags = [
    "-Wheader-hygiene",

    # Warns when a const char[] is converted to bool.
    "-Wstring-conversion",
  ]


> 
> But if ICU builds without disabling extra_warnings, I suppose that's a Good
> Thing :-)

[jungshik at Google, 2015-05-28 18:10:19]

https://codereview.chromium.org/1158933005/diff/1/icu.gyp
File icu.gyp (right):

https://codereview.chromium.org/1158933005/diff/1/icu.gyp#newcode200
icu.gyp:200: '-Wno-tautological-compare',
On 2015/05/28 02:33:52, Nico wrote:
> Since the .gn file doesn't have it, you might be able to remove
> -Wno-logical-op-parentheses and -Wno-tautological-compare from this target as
> well?

BUILD.gn has both of them under |config("icu_code")| section, which I guess is
applied to both icuuc and icui18n targets.

[Nico, 2015-05-28 18:26:58]

Ah, ok. lgtm!

[brettw, 2015-05-29 20:10:35]

rubberstamp lgtm

[jungshik at Google, 2015-06-01 20:57:11]

Committed patchset #1 (id:1) manually as
dbed54da22de6f31a38b67672efc5e3db31feb0e (presubmit successful).