Add CMake flag to ignore libfmt exit code so cross-building works

It is also safe to use `-DHAVE_SYSTEM_LIBFMT_EXITCODE=0` with < 10
version of libfmt, and in Debian there is currently 9.1.0.

It is also safe to have this flag when cross-compiling against a
libfmt-10+ version that has
fmtlib/fmt@44c3fe1

However, there hasn't been a libfmt release with this fix yet, so we
need to be careful to avoid libfmt 10.0.0-10.2.1.

ref:
- fmtlib/fmt#3835
- https://alioth-lists.debian.net/pipermail/pkg-mysql-maint/2024-May/017325.html

debian/control

@@ -16,7 +16,7 @@ Build-Depends: bison,
                libcurl4-openssl-dev | libcurl4-dev,
                libedit-dev,
                libedit-dev:native,
-               libfmt-dev (>= 7.0.0),
+               libfmt-dev (>= 10.2.2) | libfmt-dev (<< 10),
                libjemalloc-dev [linux-any],
                libjudy-dev,
                libkrb5-dev,

debian/rules

@@ -122,6 +122,7 @@ endif
 	    -DIGNORE_AIO_CHECK=ON \
 	    -DWITH_URING=ON \
 	    -DWITH_INNODB_SNAPPY=ON \
+			-DHAVE_SYSTEM_LIBFMT_EXITCODE=0 \
 	    -DDEB=$(DEB_VENDOR)
 
 # This is needed, otherwise 'make test' will run before binaries have been built