I'll put some info here on what I needed to build Sage on some exotic archs.

== Sage 5.13 ==

=== Raspberry Pi running Raspbian (armv6 with hard floats) ===

* Surprisingly ATLAS built without problems, surely because ATLAS tries to be smart only for ARMv7.
* for some libs (I'd say linbox or libmari(e)) the RAM was not large enough, I had to add some swap space.
* libmarie triggers an ICE in GCC. Lowering optimization to "-O0" solves the problem.
* tachyon fails to build but that's just because our install script does not even try.

=== ARMv7 board running Ubuntu 12.04 (armv7 with hard floats) ===

* ATLAS has to be tweaked to build with hard floats. Follow instructions at http://math-atlas.sourceforge.net/errata.html#armhardfp. I also had to bypass throttling detection: modify 
* pil did not build because of libjpeg misdetection (the lib is installed, the headers aren't, so pil thinks it can include jpeg support but then compiling fails, kind of like #7273). I modified setup.py so that it does not even try to detect libjpeg.

=== Sun Ultrasparc T1/2 running debian/sparc (64 bit kernel, 32 bit userland, 32 bit Sage build) ===

* Be sure to export ABI=32 so that MPIR and so on are not too smart and don't try to build 64 bit libs.
* PARI fails to build because it tries to include asm for 64 bit sparc v9 but gcc defaults to 32 bit sparc v8. Passing CFLAGS="-m32 -O3 -Wa,-xarch=v8plus -mcpu=ultrasparc  -g" solves this first issue. Then it tries to feed "-mimpure-text" to gcc which is not supported on linux anymore, modify config/get_dlld (this is fixed upstream in rev b2bc4faa4). 
* ecl fails after building the minimal initial version of ecl, lwowering the optimization to -O1 solves this.
* tachyon fails for the same stupid reason as on the raspberry pi.
* flint fails because we have to feed gcc with -mno-relax when packing shared obj. Fixed upstream at 38d45090d5e46e7237 and in 2.4.

=== Sun Ultrasparc T2 running Solaris 10 (64 bit kernel, 32 bit userland, 32 bit Sage build) ===

* Singular fails to buid because my system is oddly configured and a fix for very old versions of gcc includes some headers it should not. This is fixed upstream.
* FFLAS-FFLAPACK fails to build, don't know why yet. (The new?) ATLAS needs to be linked with "-lrt" (realtime lib), see http://trac.sagemath.org/ticket/10508?cversion=1&cnum_hist=415#comment:407.

=== Sun Ultrasparc T1/2 running debian/sparc (64 bit kernel, 32 bit userland, 64 bit Sage build) ===

* Be sure to export something like CC="gcc -m64" if your gcc builds 32 bit objects by default.
* PARI tries to feed "-mimpure-text" to gcc which is not supported on linux anymore, modify config/get_dlld (this is fixed upstream in rev b2bc4faa4). 
* tachyon fails for the same stupid reason as before.

=== Sun Ultrasparc T2 running Solaris 10 (64 bit kernel, 32 bit userland, 64 bit Sage build) ===

* Don't forget to set SAGE64=yes.
* This is not used by gcc, to build gcc pass something like CC="gcc -m64" or CFLAGS="-m64", I also had to pass GCC_CONFIGURE="--target=sparc64-sun-solaris2.10 --host=sparc64-sun-solaris2.10" to build a 64 bit compiler targetting 64 bit builds.
* Singular fails to buid because my system is oddly configured and a fix for very old versions of gcc includes some headers it should not. This is fixed upstream.
* FFLAS-FFLAPACK fails to build, don't know why yet. (The new?) ATLAS needs to be linked with "-lrt" (realtime lib), see http://trac.sagemath.org/ticket/10508?cversion=1&cnum_hist=415#comment:407.