external: add helpers for updating flextgl-generated headers.

src/MagnumExternal/OpenGL/update-flextgl.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+
+if [ "$#" -ne 1 ]; then
+    echo "Usage: $0 /path/to/flextGLgen.py"
+    exit 1
+fi
+
+cd GL
+$1 -D . -t . extensions.txt
+cd ..
+
+cd GLES2
+$1 -D . -t . extensions.txt
+$1 -D . -t Emscripten/ Emscripten/extensions.txt
+cd ..
+
+cd GLES3
+$1 -D . -t . extensions.txt
+$1 -D . -t Emscripten/ Emscripten/extensions.txt
+cd ..

src/MagnumExternal/Vulkan/update-flextgl.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+
+if [ "$#" -ne 1 ]; then
+    echo "Usage: $0 /path/to/flextGLgen.py"
+    exit 1
+fi
+
+$1 -D . -t . extensions.txt