Tests: Use -A option to pass generator platform selection

This is less verbose than defining CMAKE_GENERATOR_PLATFORM.

Tests/CMakeBuildTest.cmake.in

@@ -12,7 +12,7 @@ message("running: ${CMAKE_COMMAND}")
 execute_process(COMMAND "${CMAKE_COMMAND}"
   "@CMAKE_BUILD_TEST_SOURCE_DIR@"
   "-G@CMAKE_GENERATOR@"
-  "-DCMAKE_GENERATOR_PLATFORM=@CMAKE_GENERATOR_PLATFORM@"
+  -A "@CMAKE_GENERATOR_PLATFORM@"
   -T "@CMAKE_GENERATOR_TOOLSET@"
   WORKING_DIRECTORY "@CMAKE_BUILD_TEST_BINARY_DIR@"
   RESULT_VARIABLE RESULT)

Tests/CMakeLists.txt

@@ -1988,7 +1988,7 @@ ${CMake_BINARY_DIR}/bin/cmake -DDIR=dev -P ${CMake_SOURCE_DIR}/Utilities/Release
   # A test for ctest_build() with targets in subdirectories
   set(ctest_configure_options)
   if(CMAKE_GENERATOR_PLATFORM)
-    list(APPEND ctest_configure_options -DCMAKE_GENERATOR_PLATFORM=${CMAKE_GENERATOR_PLATFORM})
+    list(APPEND ctest_configure_options -A ${CMAKE_GENERATOR_PLATFORM})
   endif()
   if(CMAKE_GENERATOR_TOOLSET)
     list(APPEND ctest_configure_options -T ${CMAKE_GENERATOR_TOOLSET})

Tests/CMakeOnly/Test.cmake.in

@@ -9,7 +9,7 @@ file(MAKE_DIRECTORY "${binary_dir}")
 execute_process(
   COMMAND  ${CMAKE_COMMAND} ${CMAKE_ARGS}
   "${source_dir}" -G "@CMAKE_GENERATOR@"
-  -DCMAKE_GENERATOR_PLATFORM=${CMAKE_GENERATOR_PLATFORM}
+  -A "@CMAKE_GENERATOR_PLATFORM@"
   -T "@CMAKE_GENERATOR_TOOLSET@"
   WORKING_DIRECTORY "${binary_dir}"
   RESULT_VARIABLE result

Tests/CTestConfig/dashboard.cmake.in

@@ -19,7 +19,7 @@ message("cmake initial configure")
 execute_process(COMMAND ${CMAKE_COMMAND}
    ${arg}
    -G "@CMAKE_GENERATOR@"
-   -DCMAKE_GENERATOR_PLATFORM=${CMAKE_GENERATOR_PLATFORM}
+   -A "@CMAKE_GENERATOR_PLATFORM@"
    -T "@CMAKE_GENERATOR_TOOLSET@"
    ${CTEST_SOURCE_DIRECTORY}
   WORKING_DIRECTORY ${CTEST_BINARY_DIRECTORY}

Tests/ExternalProjectUpdate/ExternalProjectUpdateTest.cmake

@@ -13,7 +13,7 @@ macro(check_a_tag desired_tag resulting_sha fetch_expected)
   # Configure
   execute_process(COMMAND ${CMAKE_COMMAND}
     -G ${CMAKE_GENERATOR} -T "${CMAKE_GENERATOR_TOOLSET}"
-    -DCMAKE_GENERATOR_PLATFORM=${CMAKE_GENERATOR_PLATFORM}
+    -A "${CMAKE_GENERATOR_PLATFORM}"
     -DTEST_GIT_TAG:STRING=${desired_tag}
     ${ExternalProjectUpdate_SOURCE_DIR}
     WORKING_DIRECTORY ${ExternalProjectUpdate_BINARY_DIR}

Tests/FortranC/Flags.cmake.in

@@ -15,7 +15,7 @@ set(COMMAND)
 execute_process(
   WORKING_DIRECTORY "${bld}"
   COMMAND ${CMAKE_COMMAND} "${src}" -G "@CMAKE_GENERATOR@"
-                           "-DCMAKE_GENERATOR_PLATFORM=@CMAKE_GENERATOR_PLATFORM@"
+                           -A "@CMAKE_GENERATOR_PLATFORM@"
                            -T "@CMAKE_GENERATOR_TOOLSET@"
                            "-DFortranC_TEST_FLAGS=1"
                            "-DCMAKE_C_COMPILER=${bld}/cc.sh"

Tests/VSExternalInclude/CMakeLists.txt

@@ -20,7 +20,7 @@ make_directory("${LIB2_BINARY_DIR}")
 # generate lib1
 execute_process(
   COMMAND ${CMAKE_COMMAND} -G "${CMAKE_GENERATOR}"
-    -DCMAKE_GENERATOR_PLATFORM=${CMAKE_GENERATOR_PLATFORM}
+    -A "${CMAKE_GENERATOR_PLATFORM}"
     -T "${CMAKE_GENERATOR_TOOLSET}" "${VSExternalInclude_SOURCE_DIR}/Lib1"
   WORKING_DIRECTORY ${LIB1_BINARY_DIR}
   OUTPUT_VARIABLE OUT
@@ -31,7 +31,7 @@ message("CMAKE Ran with the following output:\n\"${OUT}\"")
 # generate lib2
 execute_process(
   COMMAND ${CMAKE_COMMAND} -G "${CMAKE_GENERATOR}"
-    -DCMAKE_GENERATOR_PLATFORM=${CMAKE_GENERATOR_PLATFORM}
+    -A "${CMAKE_GENERATOR_PLATFORM}"
     -T "${CMAKE_GENERATOR_TOOLSET}" "${VSExternalInclude_SOURCE_DIR}/Lib2"
   WORKING_DIRECTORY ${LIB2_BINARY_DIR}
   OUTPUT_VARIABLE OUT