I'll try and port (wait, no, I will port) fdlibm (actually I think that's what newlib partly uses); it would be a nice add-on with the next nSDL release.
I compiled the fdlibm sqrt routine codes with _IEEE_LIBM and __LITTLE_ENDIAN defined, and it works nicely:
The "inside *" messages are there to prove that it is indeed using the new functions and those of the math lib magically included by GCC.
Maybe the same trick could be blindly used on newlib's libm code (which should be pretty much the same).
PS: It seems that GCC includes libm even without -lm, how do I force it not to use any libraries? Using -nostdlib with ld-nspire just makes it vomit all kinds of __aeabi_* errors.
EDIT2: I did a few changes and compiled fdlibm; it should implement all functions in <math.h> and it also contains the macros (were added from newlib's <math.h> manually). If it works well it could be a more or less lightweight replacement to newlib's libm.a. Library's attached.