IWYU: Mark cmConfigure.h with pragma: keep

Also remove `#include "cmConfigure.h"` from most source files.
diff --git a/Source/cmInstallProgramsCommand.h b/Source/cmInstallProgramsCommand.h
index 242fb95..e0ecbda 100644
--- a/Source/cmInstallProgramsCommand.h
+++ b/Source/cmInstallProgramsCommand.h
@@ -3,7 +3,7 @@
 #ifndef cmInstallProgramsCommand_h
 #define cmInstallProgramsCommand_h
 
-#include "cmConfigure.h"
+#include "cmConfigure.h" // IWYU pragma: keep
 
 #include <string>
 #include <vector>