CI: Validate all defconfig files before running any builds

Currently, CI Build Jobs will validate the `defconfig` file just before compiling the NuttX Target (like `rv-virt:nsh`). This means that the Build Job might run for a while, before hitting a `defconfig` error and failing much later.

This PR updates the CI Workflow `build.yml` to validate all `defconfig` files before running any builds. This means that errors in the `defconfig` files will be flagged earlier. And the Build Job will terminate (with an error) before any build begins.

This behaviour is helpful for resolving CI Build Issues quickly. The code is derived from `[tools/testbuild.sh](http://tools/testbuild.sh)`. The enhancement was suggested here: apache#14259

.github/workflows/build.yml

@@ -181,6 +181,38 @@ jobs:
             export ARTIFACTDIR=`pwd`/buildartifacts
             git config --global --add safe.directory /github/workspace/sources/nuttx
             git config --global --add safe.directory /github/workspace/sources/apps
+
+            # Validate the defconfig files, in a clean temp unversioned folder
+            cp -r sources/nuttx sources/nuttx-validate
+            rm -rf sources/nuttx-validate/.git
+            pushd sources/nuttx-validate
+            testfile=tools/ci/testlist/${{matrix.boards}}.dat
+            echo Validating targets in $testfile
+            testlist=`grep -v -E "^(-|#)|^[C|c][M|m][A|a][K|k][E|e]" $testfile || true`          
+            for line in $testlist; do
+              firstch=${line:0:1}
+              if [ "X$firstch" == "X/" ]; then
+                dir=`echo $line | cut -d',' -f1`
+                list=`find boards$dir -name defconfig | cut -d'/' -f4,6`
+                for config in ${list}; do
+                  echo ./tools/refresh.sh --silent $config
+                  if ! ./tools/refresh.sh --silent $config; then
+                    echo Error: $config:1:1: error: $config is configured incorrectly. To fix it, run '"'tools/refresh.sh $config'"'
+                    fail=1
+                  fi
+                done
+              fi
+            done
+            popd
+            rm -rf sources/nuttx-validate
+
+            # Quit if the defconfig validation failed
+            if [[ "$fail" == "1" ]]; then
+              echo Error: $testfile:1:1: error: Quitting, defconfig validation failed for $testfile
+              exit 1
+            fi
+
+            # Build the targets
             cd sources/nuttx/tools/ci
             if [ "X${{matrix.boards}}" = "Xcodechecker" ]; then
                 ./cibuild.sh -c -A -N -R --codechecker testlist/${{matrix.boards}}.dat
@@ -385,4 +417,4 @@ jobs:
         with:
           name: msvc-builds
           path: buildartifacts/
-        continue-on-error: true
+        continue-on-error: true