<http://webkit.org/b/75605> WTF logging functions should call vprintf_stderr_common only once per line

Several of the WTF logging functions make multiple calls to vprintf_stderr_common to output a
single line of text. This results in strangely formatted output if vprintf_stderr_common is
retargeted to an output device that is message-oriented (such as ASL) rather than stream-oriented
like stderr.

Reviewed by Dan Bernstein.

* wtf/Assertions.cpp:
(vprintf_stderr_with_prefix): Helper function to prepend a given prefix on to the given format
string before handing it off to vprintf_stderr_common. This requires disabling warnings about
calling a printf-like function with a non-literal format string for this piece of code. It's
safe in this particular case as vprintf_stderr_with_prefix is only ever given a literal prefix.
(vprintf_stderr_with_trailing_newline): Helper function to append a trailling newline on to the
given format string if one does not already exist. It requires the same treatment with regards
to the non-literal format string warning.
(WTFReportAssertionFailureWithMessage): Switch to using vprintf_stderr_with_prefix.
(WTFReportBacktrace): Switch from calling fprintf directly to using fprintf_stderr_common.
(WTFReportFatalError): Switch to using vprintf_stderr_with_prefix.
(WTFReportError): Ditto.
(WTFLog): Switch to using vprintf_stderr_with_trailing_newline.
(WTFLogVerbose): Ditto.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@104124 268f45cc-cd09-0410-ab3c-d52691b4dbfc