In Go 1.11, the debug information is compressed for purpose of reduce binary size, and gdb on the Mac does not understand compressed DWARF.
The workaround is to also specify
-ldflags=-compressdwarf=false which does exactly what it claims.
To do this generally:
See discussion: https://groups.google.com/forum/#!topic/golang-nuts/LlgN1qpbRE8