[CMake] Declare all parts of *GenRegisterInfo.inc as outputs.

This tells the build system to check and regenerate the
*GenRegisterInfo*.inc files, should any of them be missing for
whatever reason.

A follow-up from
<#167700>.

Author: kosarev

llvm/cmake/modules/TableGen.cmake

@@ -66,6 +66,16 @@ function(tablegen project ofn)
     list(APPEND LLVM_TABLEGEN_FLAGS "-omit-comments")
   endif()
 
+  set(EXTRA_OUTPUTS)
+  if("-gen-register-info" IN_LIST ARGN)
+    string(REGEX REPLACE "\\.[^.]*$" "" OUTPUT_BASENAME ${ofn})
+    list(APPEND EXTRA_OUTPUTS
+         ${CMAKE_CURRENT_BINARY_DIR}/${OUTPUT_BASENAME}Enums.inc
+         ${CMAKE_CURRENT_BINARY_DIR}/${OUTPUT_BASENAME}Header.inc
+         ${CMAKE_CURRENT_BINARY_DIR}/${OUTPUT_BASENAME}MCDesc.inc
+         ${CMAKE_CURRENT_BINARY_DIR}/${OUTPUT_BASENAME}TargetDesc.inc)
+  endif()
+
   # MSVC can't support long string literals ("long" > 65534 bytes)[1], so if there's
   # a possibility of generated tables being consumed by MSVC, generate arrays of
   # char literals, instead. If we're cross-compiling, then conservatively assume
@@ -126,7 +136,7 @@ function(tablegen project ofn)
     set(LLVM_TABLEGEN_JOB_POOL "")
   endif()
 
-  add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${ofn}
+  add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${ofn} ${EXTRA_OUTPUTS}
     COMMAND ${tablegen_exe} ${ARG_UNPARSED_ARGUMENTS}
     ${tblgen_includes}
     ${LLVM_TABLEGEN_FLAGS}

llvm/utils/TableGen/RegisterInfoEmitter.cpp

@@ -1878,6 +1878,8 @@ TableGenOutputFiles RegisterInfoEmitter::run(StringRef FilenamePrefix) {
   if (RegisterInfoDebug)
     debugDump(errs());
 
+  // The suffixes should be in sync with the tablegen function in
+  // llvm/cmake/modules/TableGen.cmake.
   return {Main,
           {{"Enums.inc", Enums},
            {"MCDesc.inc", MCDesc},