Fixes to build WebRTC for Fuchsia

1. Added WEBRTC_FUCHSIA define.
2. Added PlatformThreadId typedef for Fuchsia.
3. Updated ifdefs for _strnicmp()/strncasecmd(), so _strnicmp()
   is used on all platforms
3. Updated ifdefs in clock.cc to avoid invalid assumption that
   POSIX = LINUX || MAC .

Bug: chromium:750940
Change-Id: Id7aa98e017f467bcebb78a0b298ba91655502072
Reviewed-on: https://webrtc-review.googlesource.com/31641
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Tommi <tommi@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21233}
diff --git a/rtc_base/platform_thread.cc b/rtc_base/platform_thread.cc
index 58beed3..06aee4e 100644
--- a/rtc_base/platform_thread.cc
+++ b/rtc_base/platform_thread.cc
@@ -20,6 +20,10 @@
 #include <sys/syscall.h>
 #endif
 
+#if defined(WEBRTC_FUCHSIA)
+#include <zircon/process.h>
+#endif
+
 namespace rtc {
 
 PlatformThreadId CurrentThreadId() {
@@ -31,8 +35,10 @@
   ret = pthread_mach_thread_np(pthread_self());
 #elif defined(WEBRTC_ANDROID)
   ret = gettid();
+#elif defined(WEBRTC_FUCHSIA)
+  ret = zx_thread_self();
 #elif defined(WEBRTC_LINUX)
-  ret =  syscall(__NR_gettid);
+  ret = syscall(__NR_gettid);
 #else
   // Default implementation for nacl and solaris.
   ret = reinterpret_cast<pid_t>(pthread_self());