check for mistyped env vars

docs/Changelog.md

gcc_plugin/Makefile

gcc_plugin/afl-gcc-fast.c

include/common.h

llvm_mode/Makefile

llvm_mode/afl-clang-fast.c

src/afl-analyze.c

src/afl-common.c

src/afl-fuzz.c

src/afl-showmap.c

src/afl-tmin.c