Re: cross compiling gsl for arm cortex M4 (nrf52)

[Mark Galassi]

Dear Julius,

Your problem seems like it might have a straightforward solution.  Whenever you 
do a lot of setting of CC and CXX and LD you might also want to set 
C_INCLUDE_PATH and CPLUS_INCLUDE_PATH (and maybe when you get to linking also 
LIBRARY_PATH).

I would try finding the full path to the gsl_minmax.h file.  Let's say it's in 
/mycrosscompilearea/stuff/include/gsl/gsl_minmax.h.  Then, noting that what's 
being #included is gsl/gsl_minmax.h, and I would say something like 
C_INCLUDE_PATH=/mycrosscompilearea/stuff/include:$C_INCLUDE_PATH

And the same for LDFLAGS and (if you use C++) for CPLUS_INCLUDE_PATH.

You might also be able to put a -I option into the CFLAGS setting you are 
already using.

And I would also investigate using pkg-config -- I have not used it in 
cross-compiling, so it might not work for you, but you can set your 
PKG_CONFIG_PATH to include /mycrosscompilearea/stuff/lib/wherever_gsl.pc_is and 
then use the usual:

pkg-config gsl --cflags
pkg-config gsl --libs

Feel free to contact me further if you want to look at this together.