Fix MinGW build

Fix MinGW build
- add missing functions SignalCodeMovingGC() and MemoryBarrier()
- avoid pointer conversion/comparison warnings
- don't attempt to hide symbols with -fvisibility, MinGW doesn't support it

BUG=http://code.google.com/p/v8/issues/detail?id=949

Committed: http://code.google.com/p/v8/source/detail?r=5913

[Erik Corry, 2010-12-01 22:10:18]

Thanks for the patch.  There are a few cosmetic issues, see below.

http://codereview.chromium.org/5471001/diff/1/src/platform-win32.cc
File src/platform-win32.cc (right):

http://codereview.chromium.org/5471001/diff/1/src/platform-win32.cc#newcode209
src/platform-win32.cc:209: 
Extra blank line needed here (2 blank lines between functions).

http://codereview.chromium.org/5471001/diff/1/src/platform-win32.cc#newcode866
src/platform-win32.cc:866: intptr_t address = (intptr_t)NULL;
We don't allow C-style casts in V8.  See the Google C++ Style Guide.  I think
just putting 0 in here would be OK.

http://codereview.chromium.org/5471001/diff/1/src/platform-win32.cc#newcode872
src/platform-win32.cc:872: if (prot == PAGE_EXECUTE_READWRITE && msize >=
(size_t)Page::kPageSize) {
C-style cast

http://codereview.chromium.org/5471001/diff/1/src/platform-win32.cc#newcode882
src/platform-win32.cc:882: if (mbase == NULL && address != (intptr_t)NULL)
C-style cast

[piscisaureus, 2010-12-01 22:50:46]

You were right. I did that.
Also changed a 'long' type to int; lint complained about it and on ia32 there's
no difference anyway.

[Søren Thygesen Gjesse, 2010-12-02 15:39:37]

On 2010/12/01 22:50:46, bertbelder wrote:
> You were right. I did that.
> Also changed a 'long' type to int; lint complained about it and on ia32
there's
> no difference anyway.

Committed: http://code.google.com/p/v8/source/detail?r=5913

Thank you for the patch. Closing issue.