libvpx/ads2gas_apple.pl: prefix comment delimiter '@' with a space for clang integrated assembler.

libvpx/ads2gas_apple.pl: prefix comment delimiter '@' with a space for clang integrated assembler.

BUG=https://code.google.com/p/webrtc/issues/detail?id=2332
R=johannkoenig@google.com

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=225010

[Ami GONE FROM CHROMIUM, 2013-09-23 17:25:17]

I'm not sure why this became necessary when last week it wasn't, but it seems to
pacify clang today.

[Johann, 2013-09-23 18:30:39]

LGTM

What a strange restriction. Do you have the error message?

[Ami GONE FROM CHROMIUM, 2013-09-24 16:38:42]

On 2013/09/23 18:30:39, Johann wrote:
> LGTM
> 
> What a strange restriction. Do you have the error message?

I think the problem is that the assembler _also_ accepts @ as a syntactic
element for "variant"s, so "end-of-line" semi-colons confuse it.  I suspect that
the real fix is to strip such EOL ;'s, which smell like holdovers from C :)

Example errors:

gen/third_party/libvpx/vp9_short_idct16x16_add_neon.S:237:22: error: invalid
variant ''
    vdup.16 d16, r3@ @ duplicate cospi_16_64
                     ^
gen/third_party/libvpx/vp9_short_idct16x16_add_neon.S:325:22: error: invalid
variant ''
    vmov.s16 q15, q0@
                     ^
gen/third_party/libvpx/vp9_short_idct16x16_add_neon.S:868:21: error: invalid
variant ''
    vdup.16 d4, r3@ @ duplicate cospi_16_64
                    ^
gen/third_party/libvpx/vp9_short_idct16x16_add_neon.S:959:22: error: invalid
variant ''
    vmov.s16 q15, q0@
                     ^

[Ami GONE FROM CHROMIUM, 2013-09-24 16:46:30]

Committed patchset #1 manually as r225010 (presubmit successful).