api: Fix genheaders.py to emit valid comments (#114)

When we switched to using SPDX identifiers instead of explicit Apache
2.0 text, the resulting generated headers ended up with a nested /*
inside the license comment.
diff --git a/api/EGL/egl.h b/api/EGL/egl.h
index 2c5990c..fd835d9 100644
--- a/api/EGL/egl.h
+++ b/api/EGL/egl.h
@@ -14,7 +14,7 @@
 ** used to make the header, and the header can be found at
 **   http://www.khronos.org/registry/egl
 **
-** Khronos $Git commit SHA1: 50f5da047a $ on $Git commit date: 2020-08-13 03:59:02 -0700 $
+** Khronos $Git commit SHA1: 5a9a7e3fcb $ on $Git commit date: 2020-08-24 11:05:32 -0700 $
 */
 
 #include <EGL/eglplatform.h>
@@ -23,7 +23,7 @@
 #define EGL_EGL_PROTOTYPES 1
 #endif
 
-/* Generated on date 20200813 */
+/* Generated on date 20201001 */
 
 /* Generated C header for:
  * API: egl
diff --git a/api/EGL/eglext.h b/api/EGL/eglext.h
index 904ee84..adfa14d 100644
--- a/api/EGL/eglext.h
+++ b/api/EGL/eglext.h
@@ -14,12 +14,12 @@
 ** used to make the header, and the header can be found at
 **   http://www.khronos.org/registry/egl
 **
-** Khronos $Git commit SHA1: 50f5da047a $ on $Git commit date: 2020-08-13 03:59:02 -0700 $
+** Khronos $Git commit SHA1: 5a9a7e3fcb $ on $Git commit date: 2020-08-24 11:05:32 -0700 $
 */
 
 #include <EGL/eglplatform.h>
 
-#define EGL_EGLEXT_VERSION 20200813
+#define EGL_EGLEXT_VERSION 20201001
 
 /* Generated C header for:
  * API: egl