previous defines made conditional

tpcclibConfig.h.in

@@ -3,10 +3,18 @@
 // Enable GNU extensions
 #define _GNU_SOURCE
 // Enable Large File Support (LFS) extension; if not defined, default probably is 32 bits, but will change to 64 bits in future
+#ifndef _FILE_OFFSET_BITS
 #define _FILE_OFFSET_BITS 64
+#endif
+#ifndef _LARGEFILE_SOURCE
 #define _LARGEFILE_SOURCE
+#endif
+#ifndef _LARGEFILE64_SOURCE
 #define _LARGEFILE64_SOURCE
+#endif
+#ifndef _TIME_BITS
 #define _TIME_BITS 64
+#endif
 // the configured options and settings for tpcclib
 #define tpcclib_VERSION @tpcclib_VERSION@
 #define tpcclib_VERSION_MAJOR @tpcclib_VERSION_MAJOR@