ENH: Clarify COMPILE_DEFINITIONS separator in docs

The COMPILE_DEFINITIONS properties are semicolon-separated lists.
Make this clear in the documentation.  See issue #9199.

Source/cmMakefile.cxx

@@ -3455,7 +3455,8 @@ void cmMakefile::DefineProperties(cmake *cm)
   cm->DefineProperty
     ("COMPILE_DEFINITIONS", cmProperty::DIRECTORY,
      "Preprocessor definitions for compiling a directory's sources.",
-     "The COMPILE_DEFINITIONS property may be set to a list of preprocessor "
+     "The COMPILE_DEFINITIONS property may be set to a "
+     "semicolon-separated list of preprocessor "
      "definitions using the syntax VAR or VAR=value.  Function-style "
      "definitions are not supported.  CMake will automatically escape "
      "the value correctly for the native build system (note that CMake "

Source/cmSourceFile.cxx

@@ -395,7 +395,8 @@ void cmSourceFile::DefineProperties(cmake *cm)
   cm->DefineProperty
     ("COMPILE_DEFINITIONS", cmProperty::SOURCE_FILE,
      "Preprocessor definitions for compiling a source file.",
-     "The COMPILE_DEFINITIONS property may be set to a list of preprocessor "
+     "The COMPILE_DEFINITIONS property may be set to a "
+     "semicolon-separated list of preprocessor "
      "definitions using the syntax VAR or VAR=value.  Function-style "
      "definitions are not supported.  CMake will automatically escape "
      "the value correctly for the native build system (note that CMake "

Source/cmTarget.cxx

@@ -87,7 +87,8 @@ void cmTarget::DefineProperties(cmake *cm)
   cm->DefineProperty
     ("COMPILE_DEFINITIONS", cmProperty::TARGET,
      "Preprocessor definitions for compiling a target's sources.",
-     "The COMPILE_DEFINITIONS property may be set to a list of preprocessor "
+     "The COMPILE_DEFINITIONS property may be set to a "
+     "semicolon-separated list of preprocessor "
      "definitions using the syntax VAR or VAR=value.  Function-style "
      "definitions are not supported.  CMake will automatically escape "
      "the value correctly for the native build system (note that CMake "