contrib: qt: fix crosscompilation for GCC 6.4

This provides work arounds for:

- incomplete std::future support
- unhandled constexpr evaluation

Signed-off-by: Thomas Guillem <thomas@gllm.fr>

contrib/src/qt/0007-ANGLE-remove-static-assert-that-can-t-be-evaluated-b.patch

+From 5de8d0bf9fb22d8a2f1b648bcbf9fc5b247dbf41 Mon Sep 17 00:00:00 2001
+From: Pierre Lamot <pierre@videolabs.io>
+Date: Thu, 21 Mar 2019 14:26:17 +0100
+Subject: [PATCH 2/2] ANGLE: remove static assert that can't be evaluated by
+ gcc 6.4
+
+---
+ .../angle/src/libANGLE/renderer/d3d/FramebufferD3D.cpp        | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/src/3rdparty/angle/src/libANGLE/renderer/d3d/FramebufferD3D.cpp b/src/3rdparty/angle/src/libANGLE/renderer/d3d/FramebufferD3D.cpp
+index 3d73b2c..12a809f 100644
+--- a/src/3rdparty/angle/src/libANGLE/renderer/d3d/FramebufferD3D.cpp
++++ b/src/3rdparty/angle/src/libANGLE/renderer/d3d/FramebufferD3D.cpp
+@@ -379,8 +379,8 @@ const gl::AttachmentList &FramebufferD3D::getColorAttachmentsForRender(const gl:
+     if (mRenderer->getWorkarounds().addDummyTextureNoRenderTarget &&
+         colorAttachmentsForRender.empty())
+     {
+-        static_assert(static_cast<size_t>(activeProgramOutputs.size()) <= 32,
+-                      "Size of active program outputs should less or equal than 32.");
++        //static_assert(static_cast<size_t>(activeProgramOutputs.size()) <= 32,
++        //"Size of active program outputs should less or equal than 32.");
+         GLenum i = static_cast<GLenum>(
+             gl::ScanForward(static_cast<uint32_t>(activeProgramOutputs.bits())));
+ 
+-- 
+2.19.1
+

contrib/src/qt/0008-ANGLE-disable-ANGLE_STD_ASYNC_WORKERS-when-compiling.patch

+From 0b5fc908a3d8e24c28e72f61bf8c6242cb85ba3e Mon Sep 17 00:00:00 2001
+From: Pierre Lamot <pierre@videolabs.io>
+Date: Thu, 21 Mar 2019 16:39:41 +0100
+Subject: [PATCH] ANGLE: disable ANGLE_STD_ASYNC_WORKERS when compiling with
+ gcc/mingw as std::future<void> is not supported
+
+---
+ src/angle/src/config.pri | 3 +++
+ 1 file changed, 3 insertions(+)
+
+diff --git a/src/angle/src/config.pri b/src/angle/src/config.pri
+index 5c52128..23109cd 100644
+--- a/src/angle/src/config.pri
++++ b/src/angle/src/config.pri
+@@ -95,6 +95,9 @@ gcc {
+                             -Wno-strict-aliasing -Wno-type-limits -Wno-unused-local-typedefs
+ 
+     QMAKE_CXXFLAGS_WARN_ON = $$QMAKE_CFLAGS_WARN_ON -Wno-reorder -Wno-conversion-null -Wno-delete-non-virtual-dtor
++	!clang {
++		   DEFINES += ANGLE_STD_ASYNC_WORKERS=ANGLE_DISABLED
++	}
+ }
+ 
+ QMAKE_CXXFLAGS_DEBUG = $$QMAKE_CFLAGS_DEBUG
+-- 
+2.19.1
+

contrib/src/qt/rules.mak

@@ -35,6 +35,8 @@ ifdef HAVE_WIN32
 ifndef HAVE_WIN64
 	$(APPLY) $(SRC)/qt/0001-disable-qt_random_cpu.patch
 endif
+	$(APPLY) $(SRC)/qt/0007-ANGLE-remove-static-assert-that-can-t-be-evaluated-b.patch
+	$(APPLY) $(SRC)/qt/0008-ANGLE-disable-ANGLE_STD_ASYNC_WORKERS-when-compiling.patch
 
 ifdef HAVE_CROSS_COMPILE
 	$(APPLY) $(SRC)/qt/0003-allow-cross-compilation-of-angle-with-wine.patch