These ‘-m’ options are defined for the H8/300 implementations:
-mrelax-relax. See ld and the H8/300, for a fuller description. -mh-ms-mn-mh or -ms. -ms2600-ms. -mexr-mexr. This option is valid only for H8S targets. -mno-exr-mno-exr. This option is valid only for H8S targets. -mint32int data 32 bits by default. -malign-300-malign-300 causes them to be aligned on 2-byte boundaries. This option has no effect on the H8/300.
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Licensed under the GNU Free Documentation License, Version 1.3.
https://gcc.gnu.org/onlinedocs/gcc-5.4.0/gcc/H8_002f300-Options.html