The musl libc also has pthread_getattr_np()

--- qtwebengine/src/3rdparty/chromium/third_party/WebKit/Source/platform/heap/ThreadState.cpp	2015-06-29 22:08:50.000000000 +0200
+++ qtwebengine/src/3rdparty/chromium/third_party/WebKit/Source/platform/heap/ThreadState.cpp	2015-07-04 02:39:41.192583302 +0200
@@ -64,7 +64,7 @@
 
 static void* getStackStart()
 {
-#if defined(__GLIBC__) || OS(ANDROID) || OS(FREEBSD)
+#if defined(__GLIBC__) || OS(ANDROID) || OS(FREEBSD) || OS(LINUX_MUSL)
     pthread_attr_t attr;
     int error;
 #if OS(FREEBSD)
