[dump] Remove NDEBUG from test to enable dump methods [NFC]

Summary:
Add LLVM_FORCE_ENABLE_DUMP cmake option, and use it along with
LLVM_ENABLE_ASSERTIONS to set LLVM_ENABLE_DUMP.

Remove NDEBUG and only use LLVM_ENABLE_DUMP to enable dump methods.

Move definition of LLVM_ENABLE_DUMP from config.h to llvm-config.h so
it'll be picked up by public headers.

Differential Revision: https://reviews.llvm.org/D38406

llvm-svn: 315590
diff --git a/llvm/lib/CodeGen/LivePhysRegs.cpp b/llvm/lib/CodeGen/LivePhysRegs.cpp
index 779f601..b7a795a 100644
--- a/llvm/lib/CodeGen/LivePhysRegs.cpp
+++ b/llvm/lib/CodeGen/LivePhysRegs.cpp
@@ -130,7 +130,7 @@
   OS << "\n";
 }
 
-#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+#ifdef LLVM_ENABLE_DUMP
 LLVM_DUMP_METHOD void LivePhysRegs::dump() const {
   dbgs() << "  " << *this;
 }