When no CFLAGS are passed into autogen.sh,
f104b3ca "tdf#72987 run firebird test for little
endian only for now" (introducing AC_C_BIGENDIAN before AC_PROG_CC) caused
CFLAGS in config_host.mk to accidentally be set to -g -O2 (instead of being left
undefined).

Change-Id: I639ce74b468e7fb25a6bda97346c7f97d6b829aa
Reviewed-on: https://gerrit.libreoffice.org/67125
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>