Add references to eglmesaext.h for build to succeed.
This patch should not be necessary in the future as these
have been added to eglext.h.
See https://github.com/KhronosGroup/EGL-Registry/commit/1343ecc9f55d3e8ded6a42d7ccfd33391a1dd35f

From: Brian Woodcox <bw@InSkyData.com>
Date: March 18, 2020

--- a/configure
+++ b/configure
@@ -24156,8 +24156,9 @@
   cat >>confdefs.h <<_ACEOF
 #define HAVE_EGL_EGLEXT_H 1
 _ACEOF
- COGL_EGL_INCLUDES="$COGL_EGL_INCLUDE
-#include <EGL/eglext.h>"
+ COGL_EGL_INCLUDES="$COGL_EGL_INCLUDES
+#include <EGL/eglext.h>
+#include <EGL/eglmesaext.h>"
 fi
 
 done
@@ -25565,8 +25566,8 @@
 fi
 
         COGL_EGL_INCLUDES="#include <EGL/egl.h>
-#include <EGL/eglext.h>"
-
+#include <EGL/eglext.h>
+#include <EGL/eglmesaext.h>"
 
 fi
 
--- a/configure.ac
+++ b/configure.ac
@@ -685,10 +685,15 @@
             AC_SUBST([COGL_EGL_INCLUDES])
 
             AC_CHECK_HEADERS([EGL/eglext.h],
-                             [COGL_EGL_INCLUDES="$COGL_EGL_INCLUDE
+                             [COGL_EGL_INCLUDES="$COGL_EGL_INCLUDES
 #include <EGL/eglext.h>"],
                              [],
                              [$COGL_EGL_INCLUDES])
+            AC_CHECK_HEADERS([EGL/eglmesaext.h],
+                             [COGL_EGL_INCLUDES="$COGL_EGL_INCLUDES
+#include <EGL/eglmesaext.h>"],
+                             [],
+                             [$COGL_EGL_INCLUDES])
 
             # Check for a GLES 1.x Common Profile library with/without EGL.
             #
@@ -1216,6 +1221,13 @@
               [],
               [AC_MSG_ERROR([Unable to locate required EGL headers])],
               [#include <EGL/egl.h>])
+            AC_CHECK_HEADERS(
+              [EGL/eglmesaext.h],
+              [],
+              [AC_MSG_ERROR([Unable to locate required EGL headers])],
+              [#include <EGL/egl.h>
+#include <EGL/eglext.h>
+#include <EGL/eglmesaext.h>])
 
             AC_CHECK_LIB(EGL, [eglInitialize],
               [COGL_EXTRA_LDFLAGS="$COGL_EXTRA_LDFLAGS -lEGL"],
@@ -1226,7 +1238,8 @@
           )
 
         COGL_EGL_INCLUDES="#include <EGL/egl.h>
-#include <EGL/eglext.h>"
+#include <EGL/eglext.h>
+#include <EGL/eglmesaext.h>"
         AC_SUBST([COGL_EGL_INCLUDES])
       ])