[CI] Only run normal check targets if requested (#168412)

When building just the runtimes (eg a patch only touches compiler-rt),
we do not actually run any normal check targets. This ends up causing an
empty ninja invocation, which builds more targets than necessary. Gate
the ninja build for normal check-* targets under an if statement to fix
this.

Author: boomanaiden154

.ci/monolithic-linux.sh

@@ -64,9 +64,11 @@ cmake -S "${MONOREPO_ROOT}"/llvm -B "${BUILD_DIR}" \
 
 start-group "ninja"
 
-# Targets are not escaped as they are passed as separate arguments.
-ninja -C "${BUILD_DIR}" -k 0 ${targets} |& tee ninja.log
-cp ${BUILD_DIR}/.ninja_log ninja.ninja_log
+if [[ "${targets}" != "" ]]; then
+  # Targets are not escaped as they are passed as separate arguments.
+  ninja -C "${BUILD_DIR}" -k 0 ${targets} |& tee ninja.log
+  cp ${BUILD_DIR}/.ninja_log ninja.ninja_log
+fi
 
 if [[ "${runtime_targets}" != "" ]]; then
   start-group "ninja Runtimes"

.ci/monolithic-windows.sh

@@ -51,9 +51,11 @@ cmake -S "${MONOREPO_ROOT}"/llvm -B "${BUILD_DIR}" \
 
 start-group "ninja"
 
-# Targets are not escaped as they are passed as separate arguments.
-ninja -C "${BUILD_DIR}" -k 0 ${targets} |& tee ninja.log
-cp ${BUILD_DIR}/.ninja_log ninja.ninja_log
+if [[ "${targets}" != "" ]]; then
+  # Targets are not escaped as they are passed as separate arguments.
+  ninja -C "${BUILD_DIR}" -k 0 ${targets} |& tee ninja.log
+  cp ${BUILD_DIR}/.ninja_log ninja.ninja_log
+fi
 
 if [[ "${runtimes_targets}" != "" ]]; then
   start-group "ninja runtimes"