{build|unit}-test: show meson-log.txt when meson fails

to make it easier to figure out why it fails.

For example in https://github.com/systemd/systemd/runs/4799774735?check_suite_focus=true
it failed with
```

meson.build:1003:8: ERROR: Command "/usr/bin/clang -print-targets" failed with status 1.

A full log can be found at /home/runner/work/systemd/systemd/build/meson-logs/meson-log.txt
Error: Process completed with exit code 1.
```
and it wasn't clear what exactly happened there.

.github/workflows/build_test.sh

@@ -125,10 +125,11 @@ for args in "${ARGS[@]}"; do
          meson -Dtests=unsafe -Dslow-tests=true -Dfuzz-tests=true --werror \
                -Dcryptolib="${CRYPTOLIB:?}" $args build; then
 
+        cat build/meson-logs/meson-log.txt
         fatal "meson failed with $args"
     fi
 
-    if ! meson compile -C build; then
+    if ! meson compile -C build -v; then
         fatal "'meson compile' failed with $args"
     fi