render/gles2: validate shaders at build time

Use glslang to validate GLSL shaders at build time. This is
optional: if glslang is not found, shader validation is skipped.

render/gles2/meson.build

@@ -4,6 +4,8 @@ if not (glesv2.found() and internal_features['egl'])
 	subdir_done()
 endif
 
+glslang = find_program('glslang', 'glslangValidator', native: true, required: false, disabler: true)
+
 features += { 'gles2-renderer': true }
 wlr_deps += glesv2
 

render/gles2/shaders/meson.build

@@ -9,6 +9,14 @@ shaders = [
 ]
 
 foreach name : shaders
+	custom_target(
+		'gles2-' + name,
+		input: name,
+		output: name + '_check',
+		command: [glslang, '@INPUT@'],
+		build_by_default: true,
+	)
+
 	output = name.underscorify() + '_src.h'
 	var = name.underscorify() + '_src'
 	wlr_files += custom_target(