Update ZPlainFirebird21 for Mac OSX

[laguna]

This code support Firebird in Mac OSX

{$ifdef Unix}
{$ifdef Darwin}
// Darwin is the base OS name of Mac OS X, like NT is the name of the Win2k/XP/Vista kernel. Mac OS X = Darwin + GUI.
LINUX1_DLL_LOCATION = 'libfbclient.dylib';
LINUX1_DLL_LOCATION_EMBEDDED = 'libfbclient.dylib';
LINUX1_IB_CRYPT_LOCATION = 'libcrypto.dylib';
{$else}
// All Unix like
LINUX1_DLL_LOCATION = 'libfbclient.so.21';
LINUX1_DLL_LOCATION_EMBEDDED = 'libfbembed.so.21';
LINUX1_IB_CRYPT_LOCATION = 'libcrypt.so.21';
{$endif}
{$endif}