Leave 'linux' defined on mips/mips64, like arm.

Change-Id: Idf1e781c34d45d1e20b7e5542d79201ae93668fe
diff --git a/core/combo/TARGET_linux-mips.mk b/core/combo/TARGET_linux-mips.mk
index 27304ee..ba03b5d 100644
--- a/core/combo/TARGET_linux-mips.mk
+++ b/core/combo/TARGET_linux-mips.mk
@@ -82,7 +82,7 @@
 
 $(combo_2nd_arch_prefix)TARGET_GLOBAL_CFLAGS += \
 			$(TARGET_mips_CFLAGS) \
-			-Ulinux -U__unix -U__unix__ -Umips \
+			-U__unix -U__unix__ -Umips \
 			-fpic -fPIE\
 			-ffunction-sections \
 			-fdata-sections \
diff --git a/core/combo/TARGET_linux-mips64.mk b/core/combo/TARGET_linux-mips64.mk
index 36b70ad..969ba10a 100644
--- a/core/combo/TARGET_linux-mips64.mk
+++ b/core/combo/TARGET_linux-mips64.mk
@@ -87,7 +87,7 @@
 
 TARGET_GLOBAL_CFLAGS += \
 			$(TARGET_mips_CFLAGS) \
-			-Ulinux -U__unix -U__unix__ -Umips \
+			-U__unix -U__unix__ -Umips \
 			-fpic -fPIE\
 			-ffunction-sections \
 			-fdata-sections \