Building 1808, I got a few errors like: /usr/bin/ld: apl-QR_factorization_GSL.o: in function `GSL::QR_factorize_ZZ_matrix(Value&, int, int, Cell const*)': QR_factorization_GSL.cc:(.text+0x97b): undefined reference to `gsl_linalg_complex_QR_decomp_r'
Turned out that ./configure was picking up an older version of libgsl (probably in /usr/lib64 from my original installation rather than my update in /usr/local/lib). Almost certainly my own fault for being careless with updates, but, if anyone else has the same problem, it's easily fixed with:
./configure --with-gsl=/usr/local/lib or wherever you keep your updates.
