Tests: Extend RunCMake.CommandLine to cover --build with no arg

Tests/RunCMake/CommandLine/RunCMakeTest.cmake

@@ -22,6 +22,8 @@ run_cmake_command(G_bad-arg ${CMAKE_COMMAND} -G NoSuchGenerator)
 run_cmake_command(P_no-arg ${CMAKE_COMMAND} -P)
 run_cmake_command(P_no-file ${CMAKE_COMMAND} -P nosuchscriptfile.cmake)
 
+run_cmake_command(build-no-dir
+  ${CMAKE_COMMAND} --build)
 run_cmake_command(build-no-cache
   ${CMAKE_COMMAND} --build ${RunCMake_SOURCE_DIR})
 run_cmake_command(build-no-generator

Tests/RunCMake/CommandLine/build-no-dir-result.txt

@@ -0,0 +1 @@
+1

Tests/RunCMake/CommandLine/build-no-dir-stderr.txt

@@ -0,0 +1 @@
+^Usage: cmake --build <dir> \[options\] \[-- \[native-options\]\]