xapian: fix build for version 1.4.5. (#2633)
xapian: fix build for version 1.4.5. (#2633)

Undef HAVE_EXP10 and HAVE___EXP10 in config.h to workaround
an incorrect detection of exp10 which libroot does not have.

Begasus/haikuports,Begasus/haikuports,haikuports/haikuports,moochris/haikuports,moochris/haikuports,haikuports/haikuports,haikuports/haikuports,haikuports/haikuports,nielx/haikuports,nielx/haikuports,nielx/haikuports,moochris/haikuports,haikuports/haikuports,Begasus/haikuports,Begasus/haikuports,Begasus/haikuports