Fix 'signedness' warning message in tracepoint_format_parser.cpp
Fix 'signedness' warning message in tracepoint_format_parser.cpp

Fix the following warning message:

/devel/bpftrace/src/tracepoint_format_parser.cpp: In static member
function ‘static bool
bpftrace::TracepointFormatParser::parse(bpftrace::ast::Program*)’:
/devel/bpftrace/src/tracepoint_format_parser.cpp:70:29: warning:
comparison of integer expressions of different signedness: ‘int’ and
‘size_t’ {aka ‘long unsigned int’} [-Wsign-compare]
           for (int i = 0; i < glob_result.gl_pathc; ++i) {
                           ~~^~~~~~~~~~~~~~~~~~~~~~

iovisor/bpftrace,iovisor/bpftrace,iovisor/bpftrace,iovisor/bpftrace