Hide uninstall target unless YAML_CPP_INSTALL is set, and allow it to…

… be disabled by YAML_CPP_DISABLE_UNINSTALL

add_custom_target uninstall causes a clash with the same target in rtmidi (https://github.com/thestk/rtmidi).
"add_custom_target cannot create target "uninstall" because another target with the same name already exists.  The existing target is a custom target created in source directory"

Adds new option YAML_CPP_DISABLE_UNINSTALL 

fixes #1151

---------

Co-authored-by: Megamouse <studienricky89@googlemail.de>
Co-authored-by: Jesse Beder <jbeder+github@gmail.com>

CMakeLists.txt

@@ -26,6 +26,8 @@ option(YAML_CPP_BUILD_TOOLS "Enable parse tools" ON)
 option(YAML_BUILD_SHARED_LIBS "Build yaml-cpp shared library" ${BUILD_SHARED_LIBS})
 option(YAML_CPP_INSTALL "Enable generation of yaml-cpp install targets" ${YAML_CPP_MAIN_PROJECT})
 option(YAML_CPP_FORMAT_SOURCE "Format source" ${YAML_CPP_MAIN_PROJECT})
+option(YAML_CPP_DISABLE_UNINSTALL "Disable uninstallation of yaml-cpp" OFF)
+
 cmake_dependent_option(YAML_CPP_BUILD_TESTS
  "Enable yaml-cpp tests" OFF
  "BUILD_TESTING;YAML_CPP_MAIN_PROJECT" OFF)
@@ -197,7 +199,7 @@ if (YAML_CPP_FORMAT_SOURCE AND YAML_CPP_CLANG_FORMAT_EXE)
 endif()
 
 # uninstall target
-if(NOT TARGET uninstall)
+if(YAML_CPP_INSTALL AND NOT YAML_CPP_DISABLE_UNINSTALL AND NOT TARGET uninstall)
  configure_file(
  "${CMAKE_CURRENT_SOURCE_DIR}/cmake_uninstall.cmake.in"
  "${CMAKE_CURRENT_BINARY_DIR}/cmake_uninstall.cmake"