apparently GMP is installed as libgmp2.a on Debian systems.
#
dnl ** check whether this machine has GMP 2.0 installed
#
-AC_CHECK_LIB(gmp, mpz_fdiv_qr, HaveLibGmp=YES, HaveLibGmp=NO)
+AC_CHECK_LIB(gmp, mpz_fdiv_qr, HaveLibGmp=YES; LibGmp=gmp,
+ AC_CHECK_LIB(gmp2, mpz_fdiv_qr, HaveLibGmp=YES; LibGmp=gmp2,
+ HaveLibGmp=No; LibGmp=not-installed))
AC_SUBST(HaveLibGmp)
+AC_SUBST(LibGmp)
#
dnl ** check whether this machine has BFD and liberty installed (used for debugging)