Drop USE_GCC and add missing build dependency

Backport an upstream commit that fixes the build with clang, which allows us to
drop USE_GCC. It is broken on at least FreeBSD 10:

    ===>  Configuring for flameshot-0.5.0
    Project ERROR: Cannot run compiler 'g++'. Output:
    ===================
    g++: not found
    ===================
    Maybe you forgot to setup the environment?
    *** Error code 3

Also add a dependency on qt5-buildtools, otherwise the build complains that rcc
is not found.

Approved by:	portmgr (antoine)
Differential Revision:	https://reviews.freebsd.org/D14100

deskutils/flameshot/Makefile

@@ -4,6 +4,7 @@
 PORTNAME=	flameshot
 PORTVERSION=	0.5.0
 DISTVERSIONPREFIX=	v
+PORTREVISION=	1
 CATEGORIES=	deskutils
 
 MAINTAINER=	nivit@FreeBSD.org
@@ -17,10 +18,10 @@ GH_ACCOUNT=	lupoDharkael
 INSTALL_ICONS=	yes
 
 USES=		qmake
-USE_GCC=	yes
 USE_GITHUB=	yes
 USE_GL=		gl
-USE_QT5=	core dbus gui linguist network widgets
+USE_QT5=	core dbus gui linguist network widgets \
+		buildtools_build
 
 post-patch:
 		@${REINPLACE_CMD} -e 's,%%LOCALBASE%%,${LOCALBASE},1' \

deskutils/flameshot/files/patch-git_481069

@@ -0,0 +1,25 @@
+From 48106975fb120fa7b6b1abb136183cb84bc957c9 Mon Sep 17 00:00:00 2001
+From: Peter Schuller <peter.schuller@infidyne.com>
+Date: Mon, 22 Jan 2018 12:15:21 -0800
+Subject: [PATCH] Fix case statement (so we build with clang). (#101)
+
+--- src/utils/screengrabber.cpp.orig	2017-12-20 13:41:48 UTC
++++ src/utils/screengrabber.cpp
+@@ -35,7 +35,7 @@ QPixmap ScreenGrabber::grabEntireDesktop(bool &ok) {
+         QPixmap res;
+ 		// handle screenshot based on DE
+         switch (m_info.windowManager()) {
+-		case m_info.GNOME: {
++		case DesktopInfo::GNOME: {
+             // https://github.com/GNOME/gnome-shell/blob/695bfb96160033be55cfb5ac41c121998f98c328/data/org.gnome.Shell.Screenshot.xml
+ 			QString path = FileNameHandler().generateAbsolutePath("/tmp") + ".png";
+ 			QDBusInterface gnomeInterface(QStringLiteral("org.gnome.Shell"),
+@@ -48,7 +48,7 @@ QPixmap ScreenGrabber::grabEntireDesktop(bool &ok) {
+ 				ok = false;
+ 			}
+             break;
+-		} case m_info.KDE: {
++		} case DesktopInfo::KDE: {
+             // https://github.com/KDE/spectacle/blob/517a7baf46a4ca0a45f32fd3f2b1b7210b180134/src/PlatformBackends/KWinWaylandImageGrabber.cpp#L145
+ 			QDBusInterface kwinInterface(QStringLiteral("org.kde.KWin"),
+ 										 QStringLiteral("/Screenshot"),