[GTK] Build broken with USE_GBM=OFF

[aperezdc]

6af38ff

[GTK] Build broken with USE_GBM=OFF
https://bugs.webkit.org/show_bug.cgi?id=271525

Reviewed by Michael Catanzaro.

Add missing USE(GBM) guards, arrange to link against libdrm with
USE_GBM=OFF and USE_LIBDRM=ON, and while at it convert the the libdrm
CMake find-module to use imported targets.

* Source/WebCore/PlatformGTK.cmake: Link libgbm or libdrm as appropriate.
* Source/WebCore/PlatformWPE.cmake: Ditto.
* Source/WebKit/PlatformGTK.cmake: Remove explicit libdrm linking, now
using an imported target it gets pulled transitively due to WebKit
linking against the WebCore target.
* Source/WebKit/PlatformWPE.cmake: Ditto.
* Source/WebKit/WPEPlatform/CMakeLists.txt: Link libgbm of libdrm as
appropriate, remove specifying the libdrm include directory for
GObject-Introspection as it gets pulled from transitively from the
imported target.
* Source/WebKit/WebProcess/WebPage/dmabuf/AcceleratedSurfaceDMABuf.cpp:
(WebKit::AcceleratedSurfaceDMABuf::backgroundColorDidChange): Add
missing USE(GBM) guard on usage of SwapChain::Type::EGLImage.
* Source/WebKit/WebProcess/WebPage/dmabuf/AcceleratedSurfaceDMABuf.h:
Only define SwapChain::Type::EGLImage with USE(GBM).
* Source/cmake/FindGBM.cmake: Make the GBM::GBM target INTERFACE-depend
on the LibDRM::LibDRM target, because headers from the former include
headers from the latter.
* Source/cmake/FindLibDRM.cmake: Convert to use imported targets, this
is needed to make GBM::GBM depend on it, and simplifies CMake build
files all around.
* Source/cmake/OptionsGTK.cmake: Use LibDRM_FOUND instead of LIBDRM_FOUND.
* Source/cmake/OptionsWPE.cmake: Ditto.

Canonical link: https://commits.webkit.org/276612@main

7a6e966

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	❌ 🧪 wpe-wk2
✅ 🧪 webkitperl	❌ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🛠 wpe-skia
✅ 🛠 🧪 jsc	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🛠 gtk
✅ 🛠 🧪 jsc-arm64	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 tv-sim		✅ 🧪 api-gtk
	✅ 🛠 watch		✅ 🛠 jsc-armv7
✅ 🛠 🧪 unsafe-merge	✅ 🛠 watch-sim		✅ 🧪 jsc-armv7-tests

[webkit-early-warning-system]

EWS run on current version of this PR (hash 7a6e966)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	❌ 🧪 wpe-wk2
✅ 🧪 webkitperl	❌ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🛠 wpe-skia
✅ 🛠 🧪 jsc	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🛠 gtk
✅ 🛠 🧪 jsc-arm64	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 tv-sim		✅ 🧪 api-gtk
	✅ 🛠 watch		✅ 🛠 jsc-armv7
✅ 🛠 🧪 unsafe-merge	✅ 🛠 watch-sim		✅ 🧪 jsc-armv7-tests

[webkit-commit-queue]

Committed 276612@main (6af38ff): https://commits.webkit.org/276612@main

Reviewed commits have been landed. Closing PR #26379 and removing active labels.