Set LIBSONAME suffix to .a for AIX

another fix for #1803

Makefile.system

@@ -1211,7 +1211,11 @@ endif
 
 LIBDLLNAME   = $(LIBPREFIX).dll
 IMPLIBNAME   = lib$(LIBNAMEBASE).dll.a
+ifneq ($(OSNAME), AIX)
 LIBSONAME    = $(LIBNAME:.$(LIBSUFFIX)=.so)
+else
+LIBSONAME    = $(LIBNAME:.$(LIBSUFFIX)=.a)
+endif
 LIBDYNNAME   = $(LIBNAME:.$(LIBSUFFIX)=.dylib)
 LIBDEFNAME   = $(LIBNAME:.$(LIBSUFFIX)=.def)
 LIBEXPNAME   = $(LIBNAME:.$(LIBSUFFIX)=.exp)