Fix compile error and host string parsing on macOS

[turley]

This fixes an error when compiling under recent versions of macOS (wrong type passed to mkdir).

It also fixes a network connection error that looks like:

Failed to connect
libsacdread: Can't open x.x.x.x:2002 for reading

The original substr(target, 0, strchr(target, ':') - target) was causing the host/ip string to be truncated (at least on macOS), so it wasn't able to connect to the actual host.

[chris-l-waters]

changing this gets me further down the road of compiling, but not past the gate.

user@Mac-mini sacd_extract % make
[  2%] Linking C executable sacd_extract
ld: warning: alignment (1) of atom '_ServerRequest_fields' (/Users/user/Downloads/sacd-ripper-master/tools/sacd_extract/CMakeFiles/sacd_extract.dir/Users/user/Downloads/sacd-ripper-master/libs/libsacd/sacd_ripper.pb.c.o) is too small and may result in unaligned pointers 
ld: pointer not aligned in '_ServerRequest_fields'+0x1A (/Users/user/Downloads/sacd-ripper-master/tools/sacd_extract/CMakeFiles/sacd_extract.dir/Users/user/Downloads/sacd-ripper-master/libs/libsacd/sacd_ripper.pb.c.o)
cc: error: linker command failed with exit code 1 (use -v to see invocation)

M4 mac mini.

[turley]

@chris-l-waters That appears to be the issue described in #12. You might have luck trying the suggestions there, but I got past it by doing MACOSX_DEPLOYMENT_TARGET=11 make