These ‘-m’ options are defined for the VAX:
-munix
Do not output certain jump instructions (aobleq
and so on) that the Unix assembler for the VAX cannot handle across long ranges.
-mgnu
Do output those jump instructions, on the assumption that the GNU assembler is being used.
-mg
Output code for G-format floating-point numbers instead of D-format.
© Free Software Foundation
Licensed under the GNU Free Documentation License, Version 1.3.
https://gcc.gnu.org/onlinedocs/gcc-7.2.0/gcc/VAX-Options.html