removed build.vc12, build.vc14 and build.vc15

Makefile.am

build.vc12/Makefile.am

build.vc12/assembler/Makefile.am

build.vc12/assembler/a_win32a_mulredc.asm

build.vc12/assembler/a_win32a_redc.asm

build.vc12/assembler/a_win32p_mulredc.asm

build.vc12/assembler/a_win32p_redc.asm

build.vc12/assembler/a_x64_mulredc.asm

build.vc12/assembler/a_x64_redc.asm

build.vc12/assembler/mulredc.asm

build.vc12/assembler/mulredc.h

build.vc12/assembler/redc.asm

build.vc12/assembler/test_mulredc.c

build.vc12/bench_mulredc/Makefile.am

build.vc12/bench_mulredc/bench_mulredc.vcxproj

build.vc12/bench_mulredc/bench_mulredc.vcxproj.filters

build.vc12/config.h

build.vc12/ecm.sln

build.vc12/ecm/Makefile.am

build.vc12/ecm/ecm.vcxproj