c: properly fixes gles2 loader

closes: Dav1dde#387

glad/generator/c/templates/loader/gles2.c

@@ -5,6 +5,7 @@
 
 #if GLAD_PLATFORM_EMSCRIPTEN
 #ifndef GLAD_EGL_H_
+  typedef void (*__eglMustCastToProperFunctionPointerType)(void);
   typedef __eglMustCastToProperFunctionPointerType (GLAD_API_PTR *PFNEGLGETPROCADDRESSPROC)(const char *name);
 #endif
   extern __eglMustCastToProperFunctionPointerType emscripten_GetProcAddress(const char *name);

test/c/compile/gles2/default/003/test.c

@@ -7,11 +7,18 @@
  * RUN: $tmp/test
  */
 
+#include <stddef.h>
+
 #define GLAD_GLES2_IMPLEMENTATION
 #define GLAD_PLATFORM_EMSCRIPTEN 1
-#include <glad/egl.h>
+#include <glad/egl.h> /* egl before gles2 */
 #include <glad/gles2.h>
 
+__eglMustCastToProperFunctionPointerType emscripten_GetProcAddress(const char *name) {
+    GLAD_UNUSED(name);
+    return GLAD_GNUC_EXTENSION (__eglMustCastToProperFunctionPointerType) NULL;
+}
+
 int main(void) {
     return 0;
 }

test/c/compile/gles2/default/004/test.c

@@ -0,0 +1,28 @@
+/*
+ * Emscripten GLES2 + header only. See also 003.
+ * Related Issues: #387
+ *
+ * GLAD: $GLAD --out-path=$tmp --api="egl,gles2" c --loader --header-only
+ * COMPILE: $GCC $test -o $tmp/test -I$tmp/include -ldl -Wno-pedantic
+ * RUN: $tmp/test
+ */
+
+#include <stddef.h>
+
+#define GLAD_GLES2_IMPLEMENTATION
+#define GLAD_PLATFORM_EMSCRIPTEN 1
+#include <glad/gles2.h>
+/*
+ * egl after gles2
+ * this is not correct, that's why we disable pedantic but it should still compile without
+ */
+#include <glad/egl.h>
+
+__eglMustCastToProperFunctionPointerType emscripten_GetProcAddress(const char *name) {
+    GLAD_UNUSED(name);
+    return GLAD_GNUC_EXTENSION (__eglMustCastToProperFunctionPointerType) NULL;
+}
+
+int main(void) {
+    return 0;
+}

test/c/compile/gles2/default/005/test.c

@@ -0,0 +1,23 @@
+/*
+ * Emscripten GLES2 + header only. See also 003.
+ * Related Issues: #387
+ *
+ * GLAD: $GLAD --out-path=$tmp --api="gles2" c --loader --header-only
+ * COMPILE: $GCC $test -o $tmp/test -I$tmp/include -ldl
+ * RUN: $tmp/test
+ */
+
+#include <stddef.h>
+
+#define GLAD_GLES2_IMPLEMENTATION
+#define GLAD_PLATFORM_EMSCRIPTEN 1
+#include <glad/gles2.h>
+
+__eglMustCastToProperFunctionPointerType emscripten_GetProcAddress(const char *name) {
+    GLAD_UNUSED(name);
+    return GLAD_GNUC_EXTENSION (__eglMustCastToProperFunctionPointerType) NULL;
+}
+
+int main(void) {
+    return 0;
+}