Tests/RunCMake/CXXModules: mask scanning checks without control

In Visual Studio, there is no mechanism to tell scanning apart from
non-scanning, so skip the sanity checks.

Tests/RunCMake/CXXModules/examples/scan_properties-stderr.txt

@@ -1,4 +1,4 @@
-CMake Warning \(dev\) at CMakeLists.txt:20 \(target_sources\):
+CMake Warning \(dev\) at CMakeLists.txt:25 \(target_sources\):
   CMake's C\+\+ module support is experimental.  It is meant only for
   experimentation and feedback to CMake developers.
 This warning is for project developers.  Use -Wno-dev to suppress it.

Tests/RunCMake/CXXModules/examples/scan_properties/CMakeLists.txt

@@ -3,6 +3,11 @@ project(scan_properties CXX)
 
 include("${CMAKE_SOURCE_DIR}/../cxx-modules-rules.cmake")
 
+set(scanning_control 1)
+if (CMAKE_GENERATOR MATCHES "Visual Studio")
+  set(scanning_control 0)
+endif ()
+
 # To detect that not-to-be scanned sources are not scanned, add a `-D` to the
 # scan flags so that the files can detect whether scanning happened and error
 # if not.
@@ -31,6 +36,7 @@ target_sources(scans_everything
         module.cxx)
 target_compile_features(scans_everything PRIVATE cxx_std_20)
 target_compile_definitions(scans_everything PRIVATE SCAN_AT_TARGET_LEVEL=1)
+target_compile_definitions(scans_everything PRIVATE "SCANNING_CONTROL=${scanning_control}")
 
 set(CMAKE_CXX_SCAN_FOR_MODULES 0)
 
@@ -49,6 +55,7 @@ target_sources(no_scan_everything
         module.cxx)
 target_compile_features(no_scan_everything PRIVATE cxx_std_20)
 target_compile_definitions(no_scan_everything PRIVATE SCAN_AT_TARGET_LEVEL=0)
+target_compile_definitions(no_scan_everything PRIVATE "SCANNING_CONTROL=${scanning_control}")
 
 add_test(NAME scanned COMMAND scans_everything)
 add_test(NAME unscanned COMMAND no_scan_everything)

Tests/RunCMake/CXXModules/examples/scan_properties/always_scan.cxx

@@ -1,5 +1,7 @@
-#ifndef CMAKE_SCANNED_THIS_SOURCE
-#  error "This file should have been scanned"
+#if SCANNING_CONTROL
+#  ifndef CMAKE_SCANNED_THIS_SOURCE
+#    error "This file should have been scanned"
+#  endif
 #endif
 
 import M;

Tests/RunCMake/CXXModules/examples/scan_properties/join.cxx

@@ -1,10 +1,12 @@
-#if SCAN_AT_TARGET_LEVEL
-#  ifndef CMAKE_SCANNED_THIS_SOURCE
-#    error "This file should have been scanned"
-#  endif
-#else
-#  ifdef CMAKE_SCANNED_THIS_SOURCE
-#    error "This file should not have been scanned"
+#if SCANNING_CONTROL
+#  if SCAN_AT_TARGET_LEVEL
+#    ifndef CMAKE_SCANNED_THIS_SOURCE
+#      error "This file should have been scanned"
+#    endif
+#  else
+#    ifdef CMAKE_SCANNED_THIS_SOURCE
+#      error "This file should not have been scanned"
+#    endif
 #  endif
 #endif
 

Tests/RunCMake/CXXModules/examples/scan_properties/main.cxx

@@ -1,10 +1,12 @@
-#if SCAN_AT_TARGET_LEVEL
-#  ifndef CMAKE_SCANNED_THIS_SOURCE
-#    error "This file should have been scanned"
-#  endif
-#else
-#  ifdef CMAKE_SCANNED_THIS_SOURCE
-#    error "This file should not have been scanned"
+#if SCANNING_CONTROL
+#  if SCAN_AT_TARGET_LEVEL
+#    ifndef CMAKE_SCANNED_THIS_SOURCE
+#      error "This file should have been scanned"
+#    endif
+#  else
+#    ifdef CMAKE_SCANNED_THIS_SOURCE
+#      error "This file should not have been scanned"
+#    endif
 #  endif
 #endif
 

Tests/RunCMake/CXXModules/examples/scan_properties/module.cxx

@@ -1,5 +1,7 @@
-#ifndef CMAKE_SCANNED_THIS_SOURCE
-#  error "This file should have been scanned"
+#if SCANNING_CONTROL
+#  ifndef CMAKE_SCANNED_THIS_SOURCE
+#    error "This file should have been scanned"
+#  endif
 #endif
 
 export module M;

Tests/RunCMake/CXXModules/examples/scan_properties/never_scan.cxx

@@ -1,5 +1,7 @@
-#ifdef CMAKE_SCANNED_THIS_SOURCE
-#  error "This file should not have been scanned"
+#if SCANNING_CONTROL
+#  ifdef CMAKE_SCANNED_THIS_SOURCE
+#    error "This file should not have been scanned"
+#  endif
 #endif
 
 int never_scan()