SDCC compiled with program-prefix breaks .rel files generated with sdas

[dciabrin]

SDCC ships a customized asxxxx and aslink that generates extended linking information in .rel files. These information are expected by sdar when building static libraries.
However the customization is enabled at runtime based on the name of the executable, i.e. it expects the assembler and the linker to be called sdasz80 and sdld respectively. Since we compile sdcc with program-prefix, the customization is never enabled.

$ SDAS_DIAG=1 /usr/bin/z80-neogeo-ihx-sdasz80 2>/dev/null 
sdas path: /usr/bin/z80-neogeo-ihx-sdasz80
is sdas: 0

Consequently, the compiler generates incompletes .rel files, which although are good enough to be linked, cannot be used with static library generated by sdar.