build: make GBM optional

Now that the DRM backend no longer depends on GBM, we can make it
optional. The GLES2 renderer still depends on it because of our EGL
device selection.

This is useful for compositors with their own renderers, and for
compositors using the Vulkan renderer.

1 files changed, 1 insertions, 1 deletions

diff --git a/README.md b/README.md
index 418aab94..7fbd691a 100644
--- a/README.md
+++ b/README.md
@@ -45,7 +45,7 @@ Install dependencies:
 * EGL and GLESv2 (optional, for the GLES2 renderer)
 * Vulkan loader, headers and glslang (optional, for the Vulkan renderer)
 * libdrm
-* GBM
+* GBM (optional, for the GBM allocator)
 * libinput (optional, for the libinput backend)
 * xkbcommon
 * udev