Revert "[X86][mem-fold] Speed up test by not re-generating the .inc file"

This reverts commit 070233d.

It also reverts follow-ups 2588e83 and
027f60a.

Author: nico

llvm/test/TableGen/lit.local.cfg

@@ -1,3 +1,2 @@
-config.suffixes = ['.td', '.test']
+config.suffixes = ['.td']
 config.excludes = ['Common']
-config.substitutions.append(('%llvm_lib_dir', f'{config.llvm_lib_dir}'))

llvm/test/TableGen/x86-fold-tables.test renamed to llvm/test/TableGen/x86-fold-tables.td

@@ -3,5 +3,5 @@
 //      fix the vulnerable rules in X86FoldTablesEmitter.cpp until the diff is reasonable
 //   2. cp <generated_file> x86-fold-tables.inc
 
-// REQUIRES: x86-registered-target
-// RUN: diff %p/x86-fold-tables.inc %llvm_lib_dir/Target/X86/X86GenFoldTables.inc
+// RUN: llvm-tblgen -gen-x86-fold-tables -asmwriternum=1 %p/../../lib/Target/X86/X86.td -I %p/../../lib/Target/X86 -I %p/../../include -o %t
+// RUN: diff %p/x86-fold-tables.inc %t