* libltdl/ltdl.h (LTDL_STMT_START, LTDL_STMT_END): Macros for

* libltdl/ltdl.h (LTDL_STMT_START, LTDL_STMT_END):  Macros for
wrapping other macros to make a portable compound statement from
multiple C statements in the expansion.
(LTDL_SET_PRELOADED_SYMBOLS): Use the above macros to add an
extern declaration for lt_preloaded_symbols, to remove
dependency on undefined symbol from libltdl.dll on cygwin (and
other -no-undefined architectures).
* libltdl/ltdl.c (lt_preloaded_symbols): No longer defined here.