gdb: fix expat search on some hosts

[jernejsk]

If /usr/lib/libexpat.so exists on host, it's picked instead of that from LE build system. From what I can tell, this issue was present before. However, in older configure logs only warning is issued but now error is returned.

Give search path for expat explicitly. This solves issue on some hosts where expat is present in system. Previously expat was set on auto and gdb configure only printed a warning. But now that it's set to "yes" configure script fails if expat isn't found.

[dhewg]

How about this instead? https://github.com/kongen/crosstool-ng/commit/1efebce61d6ca8d0c8013bfdc1f297cf05ff0ca0

[MilhouseVH]

Prior to the bump, expat support defaulted to auto which most probably explains why it hasn't been fatal until now.

I don't have the expat libs installed on my Ubuntu build host(s), so my own builds successfully found the LE expat libs once I forced this option to be ON. Sorry, my bad.

The fix suggested by @dhewg is likely the best option, and just means the following change:

-                           --with-expat=yes \
+                           --with-expat=yes --with-libexpat-prefix=${SYSROOT_PREFIX}/usr \

in gdb/package.mk - @jernejsk can you try that?

This results in:

checking for libexpat... yes
checking how to link with libexpat... /home/ubuntu/projects/LibreELEC.tv/build.LibreELEC-RPi2.arm-9.80-devel/toolchain/armv7ve-libreelec-linux-gnueabihf/sysroot/usr/lib/libexpat.so -Wl,-rpath -Wl,/home/ubuntu/projects/LibreELEC.tv/build.LibreELEC-RPi2.arm-9.80-devel/toolchain/armv7ve-libreelec-linux-gnueabihf/sysroot/usr/lib
checking for XML_StopParser... yes

which seems to work...

Although I suspect it's somewhat unlikely anyone will need the features supported by expat:

https://sourceware.org/gdb/current/onlinedocs/gdb/Requirements.html

but since we've included it in the past, I guess we should continue...

[jernejsk]

@MilhouseVH That works, but I don't think we need it. I can give similar argument, for me (and surely for some other people) was never enabled.

[MilhouseVH]

I have no objection if you leave it disabled. :)