platform: fix build on SmartOS

With -std=g++0x, `signbit` is no longer a define, and is an actual
function declared in C++-specific headers. Thus checking it's presence
with ifdef will no longer work.

Considering that g++0x implies newer compiler, there should not be the
case where it won't be present anymore.

BUG=
R=bmeurer@chromium.org, danno

Review URL: https://codereview.chromium.org/642203003

Patch from Fedor Indutny <fedor.indutny@gmail.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24730 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/base/platform/platform-solaris.cc

@@ -31,26 +31,6 @@
 #include "src/base/platform/platform.h"
 
 
-// It seems there is a bug in some Solaris distributions (experienced in
-// SunOS 5.10 Generic_141445-09) which make it difficult or impossible to
-// access signbit() despite the availability of other C99 math functions.
-#ifndef signbit
-namespace std {
-// Test sign - usually defined in math.h
-int signbit(double x) {
-  // We need to take care of the special case of both positive and negative
-  // versions of zero.
-  if (x == 0) {
-    return fpclass(x) & FP_NZERO;
-  } else {
-    // This won't detect negative NaN but that should be okay since we don't
-    // assume that behavior.
-    return x < 0;
-  }
-}
-}  // namespace std
-#endif  // signbit
-
 namespace v8 {
 namespace base {
 

src/base/platform/platform.h

@@ -29,14 +29,6 @@
 #include "src/base/platform/mutex.h"
 #include "src/base/platform/semaphore.h"
 
-#ifdef __sun
-# ifndef signbit
-namespace std {
-int signbit(double x);
-}
-# endif
-#endif
-
 #if V8_OS_QNX
 #include "src/base/qnx-math.h"
 #endif