Binary package “libgflags-dev” in ubuntu eoan

commandline flags module for C++ (development files)

 gflags is a library that implements commandline flags processing. As
 such it's a replacement for getopt(). It has increased flexibility,
 including built-in support for C++ types like string, and the ability
 to define flags in the source file in which they're used.
 This package contains development libraries and header files.