Prepend ./ to $(PRISM_OBJS) for BSD make

Align to `$(PRISM_SRCDIR)` that begins with `$(srcdir)`.  BSD make
treats `./foo` and `foo` as different things if `foo` does not exist.

Author: nobu

common.mk

@@ -85,30 +85,30 @@ MAKE_ENC      = -f $(ENC_MK) V="$(V)" UNICODE_HDR_DIR="$(UNICODE_HDR_DIR)" \
 
 PRISM_BUILD_DIR = prism
 
-PRISM_OBJS    = prism/api_node.$(OBJEXT) \
-		prism/api_pack.$(OBJEXT) \
-		prism/diagnostic.$(OBJEXT) \
-		prism/encoding.$(OBJEXT) \
-		prism/extension.$(OBJEXT) \
-		prism/node.$(OBJEXT) \
-		prism/options.$(OBJEXT) \
-		prism/pack.$(OBJEXT) \
-		prism/prettyprint.$(OBJEXT) \
-		prism/regexp.$(OBJEXT) \
-		prism/serialize.$(OBJEXT) \
-		prism/static_literals.$(OBJEXT) \
-		prism/token_type.$(OBJEXT) \
-		prism/util/pm_buffer.$(OBJEXT) \
-		prism/util/pm_char.$(OBJEXT) \
-		prism/util/pm_constant_pool.$(OBJEXT) \
-		prism/util/pm_integer.$(OBJEXT) \
-		prism/util/pm_list.$(OBJEXT) \
-		prism/util/pm_memchr.$(OBJEXT) \
-		prism/util/pm_newline_list.$(OBJEXT) \
-		prism/util/pm_string.$(OBJEXT) \
-		prism/util/pm_strncasecmp.$(OBJEXT) \
-		prism/util/pm_strpbrk.$(OBJEXT) \
-		prism/prism.$(OBJEXT) \
+PRISM_OBJS    = ./prism/api_node.$(OBJEXT) \
+		./prism/api_pack.$(OBJEXT) \
+		./prism/diagnostic.$(OBJEXT) \
+		./prism/encoding.$(OBJEXT) \
+		./prism/extension.$(OBJEXT) \
+		./prism/node.$(OBJEXT) \
+		./prism/options.$(OBJEXT) \
+		./prism/pack.$(OBJEXT) \
+		./prism/prettyprint.$(OBJEXT) \
+		./prism/regexp.$(OBJEXT) \
+		./prism/serialize.$(OBJEXT) \
+		./prism/static_literals.$(OBJEXT) \
+		./prism/token_type.$(OBJEXT) \
+		./prism/util/pm_buffer.$(OBJEXT) \
+		./prism/util/pm_char.$(OBJEXT) \
+		./prism/util/pm_constant_pool.$(OBJEXT) \
+		./prism/util/pm_integer.$(OBJEXT) \
+		./prism/util/pm_list.$(OBJEXT) \
+		./prism/util/pm_memchr.$(OBJEXT) \
+		./prism/util/pm_newline_list.$(OBJEXT) \
+		./prism/util/pm_string.$(OBJEXT) \
+		./prism/util/pm_strncasecmp.$(OBJEXT) \
+		./prism/util/pm_strpbrk.$(OBJEXT) \
+		./prism/prism.$(OBJEXT) \
 		prism_init.$(OBJEXT)
 
 COMMONOBJS    = \