libc: extent vbox specific pthread_create API

Make it possible to adopt normal Genode::Threads for use within in a
pthread environment.

Issue #3164.

repos/libports/lib/symbols/libc

@@ -948,6 +948,7 @@ _ZN16Pthread_registry6insertEP7pthread T
 _ZN16Pthread_registry6removeEP7pthread T
 _ZN16Pthread_registry8containsEP7pthread T
 _ZN4Libc14pthread_createEPP7pthreadPFPvS3_ES3_mPKcPN6Genode11Cpu_sessionENS8_8Affinity8LocationE T
+_ZN4Libc14pthread_createEPP7pthreadRN6Genode6ThreadE T
 
 #
 # Libc plugin interface

repos/libports/src/lib/libc/thread_create.cc

@@ -37,6 +37,18 @@ int Libc::pthread_create(pthread_t *thread,
 }
 
 
+int Libc::pthread_create(pthread_t *thread, Genode::Thread &t)
+{
+		pthread_t thread_obj = new pthread(t);
+
+		if (!thread_obj)
+			return EAGAIN;
+
+		*thread = thread_obj;
+		return 0;
+}
+
+
 extern "C"
 {
 	int pthread_create(pthread_t *thread, const pthread_attr_t *attr,

repos/libports/src/lib/libc/thread_create.h

@@ -21,4 +21,6 @@ namespace Libc {
 	                   void *(*start_routine) (void *), void *arg,
 	                   size_t stack_size, char const * name,
 	                   Genode::Cpu_session * cpu, Genode::Affinity::Location location);
+
+	int pthread_create(pthread_t *, Genode::Thread &);
 }