Ok, I'm currently trying to get things running, setting up a crosscompiler toolchain for the Arduino Yun is fairly
easy, just follow the tutorial on the  OpenWrt webpage.

The main problem is that openwrt uses the uClibc library instead of glibc this produces lots of difficulties, first
one is that building of the shared library is complaining about symbol name mismatches, but I guess this can be
fixed somehow, I wont use the midas-shared library, therefore I just disabled it in the Makefile. 

The next problem is the backtrace functions tjhat are used within system.c, the functions backtrace and
backtrace_symbols are only available in glibc for a quick fix I just changed the #ifdef directive in a way that this
code is not built. 
 

There is a more tricky problem, the compiler complains about mismatched function defintions:

In file included from include/midasinc.h:17:0,
                 from include/msystem.h:35,
                 from src/sequencer.cxx:13:
/home/clemens/arduino/openwrt-yun/build_dir/toolchain-mips_r2_gcc-4.6-linaro_uClibc-0.9.33.2/uClibc-0.9.33.2/include/string.h:495:41:
error: declaration of 'size_t strlcat(char*, const char*, size_t) throw ()' has a different exception specifier
include/midas.h:1955:17: error: from previous declaration 'size_t strlcat(char*, const char*, size_t)'
/home/clemens/arduino/openwrt-yun/build_dir/toolchain-mips_r2_gcc-4.6-linaro_uClibc-0.9.33.2/uClibc-0.9.33.2/include/string.h:498:41:
error: declaration of 'size_t strlcpy(char*, const char*, size_t) throw ()' has a different exception specifier
include/midas.h:1954:17: error: from previous declaration 'size_t strlcpy(char*, const char*, size_t)'

This can be solved by editing the midas.h file:
size_t EXPRT strlcpy(char *dst, const char *src, size_t size); -> size_t EXPRT strlcpy(char *dst, const char *src,
size_t size) __THROW __nonnull ((1, 2));

and 

size_t EXPRT strlcat(char *dst, const char *src, size_t size); -> size_t EXPRT strlcat(char *dst, const char *src,
size_t size) __THROW __nonnull ((1, 2));

the same trick has to be done in ../mxml/strlcpy.h

After changing this midas compiles with the crosscompiler and the resulting programs are executable on the Arduino
Yun. I'll report back if I got my frontend to run and connect to the midas server.