[clang/Basic] Make TargetInfo.h not use DataLayout again

Reverts parts of https://reviews.llvm.org/D17183, but keeps the
resetDataLayout() API and adds an assert that checks that datalayout string and
user label prefix are in sync.

Approach 1 in https://reviews.llvm.org/D17183#2653279
Reduces number of TUs build for 'clang-format' from 689 to 575.

I also implemented approach 2 in D100764. If someone feels motivated
to make us use DataLayout more, it's easy to revert this change here
and go with D100764 instead. I don't plan on doing more work in this
area though, so I prefer going with the smaller, more self-consistent change.

Differential Revision: https://reviews.llvm.org/D100776

utils/gn/secondary/clang/lib/Basic/BUILD.gn

@@ -49,7 +49,6 @@ static_library("Basic") {
     "//clang/include/clang/Sema:AttrParsedAttrKinds",
     "//clang/include/clang/Sema:AttrSpellingListIndex",
     "//llvm/include/llvm/Config:llvm-config",
-    "//llvm/lib/IR",
     "//llvm/lib/MC",
     "//llvm/lib/Support",
   ]

utils/gn/secondary/clang/tools/clang-format/BUILD.gn

@@ -11,6 +11,7 @@ executable("clang-format") {
     "//clang/lib/AST/",
     "//clang/lib/Frontend/",
     "//clang/lib/Sema/",
+    "//llvm/lib/IR",
   ]
   sources = [ "ClangFormat.cpp" ]
 }