bug#61988: error compiling emacs

[Po Lu]

What if you try this instead?

diff --git a/configure.ac b/configure.ac
index bc7e61048c3..ac93d003b70 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2806,6 +2806,25 @@ AC_DEFUN
       WEBP_MODULE="libwebpdemux >= $WEBP_REQUIRED"
 
       EMACS_CHECK_MODULES([WEBP], [$WEBP_MODULE])
+
+      # WebPGetInfo is sometimes not present inside libwebpdemux, so
+      # if it does not link, also check for libwebpdecoder.
+
+      OLD_CFLAGS=$CFLAGS
+      OLD_LIBS=$LIBS
+      CFLAGS="$CFLAGS $WEBP_CFLAGS"
+      LIBS="$LIBS $WEBP_LIBS"
+
+      AC_CHECK_FUNC([WebPGetInfo], [],
+        [WEBP_MODULE="$WEBP_MODULE libwebpdecoder >= $WEBP_REQUIRED"
+        HAVE_WEBP=no
+        AS_UNSET([WEBP_LIBS])
+        AS_UNSET([WEBP_CFLAGS])
+        EMACS_CHECK_MODULES([WEBP], [$WEBP_MODULE])])
+
+      CFLAGS=$OLD_CFLAGS
+      LIBS=$OLD_LIBS
+
       AC_SUBST([WEBP_CFLAGS])
       AC_SUBST([WEBP_LIBS])
    fi

I'm not sure what pkg-config is doing here TBH, but it isn't very
intuitive.