configure: check for icu DEFS In some cases we need to add additional defs to build against icu if icu has certain options configured. ICU warns about this when building: *** WARNING: You must set the following flags before code compiled against this ICU will function properly: -DU_DISABLE_RENAMING=1 We can fetch these flags from the icu pkgconfig and add them if required. This fixes symbol errors if ICU is built without renaming. Signed-off-by: James Hilliard <james.hilliard1@gmail.com>