[CMake][TableGen] Remove dead CMake version checks

[tambre]

Summary

LLVM requires CMake 3.13.4, so remove version checks that are dead code.

[phosek]

LGTM

llvm/cmake/modules/TableGen.cmake

 # LLVM_TARGET_DEFINITIONS must contain the name of the .td file to process.
 # Extra parameters for `tblgen' may come after `ofn' parameter.
 # Adds the name of the generated file to TABLEGEN_OUTPUT.
 
 function(tablegen project ofn)
   # Validate calling context.
   if(NOT ${project}_TABLEGEN_EXE)
     message(FATAL_ERROR "${project}_TABLEGEN_EXE not set")
   endif()
 
-  # Use depfile instead of globbing arbitrary *.td(s)
-  # DEPFILE is available for Ninja Generator with CMake>=3.7.
-  if(CMAKE_GENERATOR STREQUAL "Ninja" AND NOT CMAKE_VERSION VERSION_LESS 3.7)
+  # Use depfile instead of globbing arbitrary *.td(s) for Ninja.
+  if(CMAKE_GENERATOR STREQUAL "Ninja")
     # Make output path relative to build.ninja, assuming located on
     # ${CMAKE_BINARY_DIR}.
     # CMake emits build targets as relative paths but Ninja doesn't identify
     # absolute path (in *.d) as relative path (in build.ninja)
     # Note that tblgen is executed on ${CMAKE_BINARY_DIR} as working directory.
     file(RELATIVE_PATH ofn_rel
       ${CMAKE_BINARY_DIR} ${CMAKE_CURRENT_BINARY_DIR}/${ofn})
     set(additional_cmdline
function(add_public_tablegen_target target)
   set_target_properties(${target} PROPERTIES FOLDER "Tablegenning")
   set(LLVM_COMMON_DEPENDS ${LLVM_COMMON_DEPENDS} ${target} PARENT_SCOPE)
 endfunction()
 
 macro(add_tablegen target project)
   set(${target}_OLD_LLVM_LINK_COMPONENTS ${LLVM_LINK_COMPONENTS})
   set(LLVM_LINK_COMPONENTS ${LLVM_LINK_COMPONENTS} TableGen)
 
-  # CMake-3.9 doesn't let compilation units depend on their dependent libraries.
-  if(NOT (CMAKE_GENERATOR STREQUAL "Ninja" AND NOT CMAKE_VERSION VERSION_LESS 3.9) AND NOT XCODE)
+  # CMake doesn't let compilation units depend on their dependent libraries on some generators.
+  if(NOT CMAKE_GENERATOR STREQUAL "Ninja" AND NOT XCODE)
     # FIXME: It leaks to user, callee of add_tablegen.
     set(LLVM_ENABLE_OBJLIB ON)
   endif()
 
   add_llvm_executable(${target} DISABLE_LLVM_LINK_LLVM_DYLIB ${ARGN})
   set(LLVM_LINK_COMPONENTS ${${target}_OLD_LLVM_LINK_COMPONENTS})
 
   set(${project}_TABLEGEN "${target}" CACHE