Allow Cygwin to build shared libs

ChangeLog

 2016-08-16  Mathis Rosenhauer  <rosenhauer@dkrz.de>
 
+	Better compatibility with OSX for make check
+
+	Allow Cygwin to build DLLs
+
 	v0.3.4
 
 	Pad incomplete last line when in SZ compatibility mode

src/Makefile.am

 lib_LTLIBRARIES = libaec.la libsz.la
 libaec_la_SOURCES = encode.c encode_accessors.c decode.c \
 encode.h encode_accessors.h decode.h
-libaec_la_LDFLAGS = -version-info 0:5:0
+libaec_la_LDFLAGS = -version-info 0:5:0 -no-undefined
 
 libsz_la_SOURCES = sz_compat.c
 libsz_la_LIBADD = libaec.la
-libsz_la_LDFLAGS = -version-info 2:1:0
+libsz_la_LDFLAGS = -version-info 2:1:0 -no-undefined
 
 include_HEADERS = libaec.h szlib.h