Issue during compilation with flex++

[jateenjoshi]

I'm trying to compile the latest on master on Ubuntu 18 with the instructions, but am running into an issue when flex++ is invoked:

> make
flex++ -+ -otools/compile/llcLexer.preproc1 tools/compile/llcLexer.l
tools/compile/llcLexer.l:12: unrecognized %option: ansi-definitions
tools/compile/llcLexer.l:13: unrecognized %option: ansi-prototypes
Variable trailing context rule at line 220
Variable trailing context rule at line 221
Variable trailing context rule at line 223
make: *** [tools/compile/module.mk:10: tools/compile/llcLexer.cpp] Error 1

flex++ version:

> flex++ --version
flex++ 2.6.4

It looks like there are two separate issues:

1. unrecognized %options
2. Variable trailing context rules on the lines mentioned

Any ideas? I've tried it with both flex++ 2.6.4 and 2.5.4