Older versions of gcc do not know about -Wno-pointer-sign.

tests/Makefile.am

 AM_CPPFLAGS = -I$(top_srcdir)/include
-AM_CFLAGS = -Wno-pointer-sign
+#AM_CFLAGS = -Wno-pointer-sign
 LDADD = $(top_builddir)/src/libyaml.la
 TESTS = test-version test-reader
 check_PROGRAMS = test-version test-reader