qt5: musl libc main thread stack bottom calc

For musl libc, just as for Android, the main thread pretends
to have a tiny stack space. Add a patch based on the one
found at: https://bugreports.qt.io/browse/QTBUG-44268

Closes #3965

srcpkgs/qt5/patches/qt-musl-stackbottom.patch

@@ -0,0 +1,26 @@
+For musl libc the stackBottom for the main thread is recalculated
+just as it is for Android. See: https://bugreports.qt.io/browse/QTBUG-44268
+
+--- qtdeclarative/src/qml/jsruntime/qv4engine.cpp	2016-02-26 10:34:34.000000000 +0100
++++ qtdeclarative/src/qml/jsruntime/qv4engine.cpp	2016-04-04 21:52:43.780823136 +0200
+@@ -94,6 +94,11 @@
+ #include <valgrind/memcheck.h>
+ #endif
+ 
++#if defined(Q_OS_LINUX) && !defined(__GLIBC__)
++#include <sys/syscall.h>
++#define gettid() syscall(SYS_gettid)
++#endif
++
+ QT_BEGIN_NAMESPACE
+ 
+ using namespace QV4;
+@@ -147,7 +152,7 @@
+         pthread_attr_getstack(&attr, &stackBottom, &stackSize);
+         pthread_attr_destroy(&attr);
+ 
+-#        if defined(Q_OS_ANDROID)
++#        if defined(Q_OS_ANDROID) || !defined(__GLIBC__)
+         // Bionic pretends that the main thread has a tiny stack; work around it
+         if (gettid() == getpid()) {
+             rlimit limit;

srcpkgs/qt5/template

@@ -1,7 +1,7 @@
 # Template file for 'qt5'
 pkgname=qt5
 version=5.6.0
-revision=4
+revision=5
 wrksrc="qt-everywhere-opensource-src-${version}"
 homepage="http://qt.io/"
 short_desc="A cross-platform application and UI framework (QT5)"