Revert "+feature compile by llvm" use CXX=clang++

This reverts commit 4453a5cd.

Conflicts:
	acompaction2/makefile
	acompare2/makefile
	aconversions2/makefile
	aconvert2/makefile
	aderivation2/makefile
	adeterminize2/makefile
	aecho2/makefile
	aepsilon2/makefile
	agenerate2/makefile
	aintegral2/makefile
	alangop2/makefile
	aminimize2/makefile
	anormalize2/makefile
	arand2/makefile
	arename2/makefile
	areverse2/makefile
	arun2/makefile
	astat2/makefile
	astringology2/makefile
	atrim2/makefile
	tniceprint/makefile