build/pkgs/iconv/spkg-configure.m4: Fix quoting bug

Author: Matthias Koeppe

build/pkgs/iconv/spkg-configure.m4

@@ -1,6 +1,6 @@
 SAGE_SPKG_CONFIGURE([iconv], [
     AM_ICONV
-    if test x$am_cv_func_iconv != xyes; then
+    if test x"$am_cv_func_iconv" != xyes; then
        sage_spkg_install_iconv=yes
     fi
 ])