patch 8.1.1687: the evalfunc.c file is too big

Problem:    The evalfunc.c file is too big.
Solution:   Move testing support to a separate file.
diff --git a/src/Make_morph.mak b/src/Make_morph.mak
index 7bd39fa..2565df5 100644
--- a/src/Make_morph.mak
+++ b/src/Make_morph.mak
@@ -81,6 +81,8 @@
 	syntax.c						\
 	tag.c							\
 	term.c							\
+	testing.c						\
+	textprop.c						\
 	ui.c							\
 	undo.c							\
 	usercmd.c						\