Revert "[clang] Increase VecLib bitfield size to 4 bits in CodeGenOptions.def" (llvm#109161)

Reverts llvm#108804

Bots are failing:
https://lab.llvm.org/buildbot/#/builders/140/builds/6859

Author: AaronBallman

clang/include/clang/Basic/CodeGenOptions.def

@@ -375,18 +375,8 @@ ENUM_CODEGENOPT(Inlining, InliningMethod, 2, NormalInlining)
 /// The maximum stack size a function can have to be considered for inlining.
 VALUE_CODEGENOPT(InlineMaxStackSize, 32, UINT_MAX)
 
-// Define the number of bits required for the VecLib enum
-#define VECLIB_BIT_COUNT (llvm::countPopulation(llvm::driver::VectorLibrary::MaxLibrary))
-
-// Ensure the VecLib bitfield has enough space for future vector libraries.
-// The number of bits is determined automatically based on the number of enum values.
-static_assert(static_cast<size_t>(llvm::driver::VectorLibrary::MaxLibrary) <= (1 << VECLIB_BIT_COUNT),
-              "VecLib bitfield size is too small to accommodate all vector libraries.");
-              
-// VecLib definition in CodeGenOptions.def
-ENUM_CODEGENOPT(VecLib, llvm::driver::VectorLibrary, VECLIB_BIT_COUNT, llvm::driver::VectorLibrary::NoLibrary)
-
-#undef VECLIB_BIT_COUNT
+// Vector functions library to use.
+ENUM_CODEGENOPT(VecLib, llvm::driver::VectorLibrary, 3, llvm::driver::VectorLibrary::NoLibrary)
 
 /// The default TLS model to use.
 ENUM_CODEGENOPT(DefaultTLSModel, TLSModel, 2, GeneralDynamicTLSModel)