Oracle's development package includes an ldap.h file that causes compilation attempts of PHP to fail.
For the oracle-instantclient12.2-devel 64-bit RPM, this file is found in the following path:
/usr/include/oracle/12.2/client64/ldap.h
Rename this file to ldap.h-oracle.
After doing so, and assuming there are no other build problems, PHP will compile (even when ldap and oci are configured in the build).