configure: only install khrplatform.h if needed

khrplatform.h is only used by EGL and GLES; let's only install it when
one of those is enabled.

Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Jussi Kukkonen <jussi.kukkonen@intel.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
diff --git a/configure.ac b/configure.ac
index 61d98e2..46fcd8f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1291,6 +1291,9 @@
 AM_CONDITIONAL(NEED_OPENGL_COMMON, test "x$enable_opengl" = xyes -o \
                                         "x$enable_gles1" = xyes -o \
                                         "x$enable_gles2" = xyes)
+AM_CONDITIONAL(NEED_KHRPLATFORM, test "x$enable_egl" = xyes -o \
+                                      "x$enable_gles1" = xyes -o \
+                                      "x$enable_gles2" = xyes)
 
 # Validate GLX options
 if test "x$enable_glx" = xyes; then