GCC8 is already used for fortran so set USES=compiler:c11 to use GCC8 for everything.
Set LDFLAGS+=-leccodes to fix:
/usr/local/bin/ld: describe_input_field.c:(.text+0x1a14): undefined reference to `grib_get_long_array'
/usr/local/bin/ld: describe_input_field.c:(.text+0x1c48): undefined reference to `grib_get_error_message'
/usr/local/bin/ld: describe_input_field.c:(.text+0x1c88): undefined reference to `grib_get_double'
PR: 239438