Use isnan from std namespace in ProfileGenerator.cpp
https://bugs.webkit.org/show_bug.cgi?id=137653

Patch by Adrien Destugues <pulkomandy@gmail.com> on 2014-10-16
Reviewed by Darin Adler.

The C++ isnan() function is in the std namespace. The unprefixed isnan
may be available because of C99 headers leakage in C++, but should not
be used.

No new tests: no functional change, build fix on platforms which don't
export C99 functions in C++.

* profiler/ProfileGenerator.cpp:
(JSC::ProfileGenerator::beginCallEntry):
(JSC::ProfileGenerator::endCallEntry):
(JSC::ProfileGenerator::didPause):
(JSC::ProfileGenerator::didContinue):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@174762 268f45cc-cd09-0410-ab3c-d52691b4dbfc