Fix asm offsets generation for universal-darwin builds

Added BUILD_PFX to correct dependencies.

Change-Id: Ia07602bd98ef2253242b1bd66ef05e3b1e64ba7d
diff --git a/libs.mk b/libs.mk
index 452c3f8..fed1847 100644
--- a/libs.mk
+++ b/libs.mk
@@ -272,20 +272,20 @@
 #
 
 ifeq ($(filter icc gcc,$(TGT_CC)), $(TGT_CC))
-    asm_com_offsets.asm: $(VP8_PREFIX)common/asm_com_offsets.c.S
+    $(BUILD_PFX)asm_com_offsets.asm: $(BUILD_PFX)$(VP8_PREFIX)common/asm_com_offsets.c.S
 	grep EQU $< | tr -d '$$\#' $(ADS2GAS) > $@
-    $(VP8_PREFIX)common/asm_com_offsets.c.S: vp8/common/asm_com_offsets.c
-    CLEAN-OBJS += asm_com_offsets.asm $(VP8_PREFIX)common/asm_com_offsets.c.S
+    $(BUILD_PFX)$(VP8_PREFIX)common/asm_com_offsets.c.S: $(VP8_PREFIX)common/asm_com_offsets.c
+    CLEAN-OBJS += $(BUILD_PFX)asm_com_offsets.asm $(BUILD_PFX)$(VP8_PREFIX)common/asm_com_offsets.c.S
 
-    asm_enc_offsets.asm: $(VP8_PREFIX)encoder/asm_enc_offsets.c.S
+    $(BUILD_PFX)asm_enc_offsets.asm: $(BUILD_PFX)$(VP8_PREFIX)encoder/asm_enc_offsets.c.S
 	grep EQU $< | tr -d '$$\#' $(ADS2GAS) > $@
-    $(VP8_PREFIX)encoder/asm_enc_offsets.c.S: vp8/encoder/asm_enc_offsets.c
-    CLEAN-OBJS += asm_enc_offsets.asm $(VP8_PREFIX)encoder/asm_enc_offsets.c.S
+    $(BUILD_PFX)$(VP8_PREFIX)encoder/asm_enc_offsets.c.S: $(VP8_PREFIX)encoder/asm_enc_offsets.c
+    CLEAN-OBJS += $(BUILD_PFX)asm_enc_offsets.asm $(BUILD_PFX)$(VP8_PREFIX)encoder/asm_enc_offsets.c.S
 
-    asm_dec_offsets.asm: $(VP8_PREFIX)decoder/asm_dec_offsets.c.S
+    $(BUILD_PFX)asm_dec_offsets.asm: $(BUILD_PFX)$(VP8_PREFIX)decoder/asm_dec_offsets.c.S
 	grep EQU $< | tr -d '$$\#' $(ADS2GAS) > $@
-    $(VP8_PREFIX)decoder/asm_dec_offsets.c.S: vp8/decoder/asm_dec_offsets.c
-    CLEAN-OBJS += asm_dec_offsets.asm $(VP8_PREFIX)decoder/asm_dec_offsets.c.S
+    $(BUILD_PFX)$(VP8_PREFIX)decoder/asm_dec_offsets.c.S: $(VP8_PREFIX)decoder/asm_dec_offsets.c
+    CLEAN-OBJS += $(BUILD_PFX)asm_dec_offsets.asm $(BUILD_PFX)$(VP8_PREFIX)decoder/asm_dec_offsets.c.S
 else
   ifeq ($(filter rvct,$(TGT_CC)), $(TGT_CC))
     asm_com_offsets.asm: obj_int_extract