Bug#886976: gcc-8: add a splash before mipsr6 etc to fix arch name recognize/

[YunQiang Su <wzssyqa@gmail.com>]

Package: src:gcc-8

Currently we missed a slash before the arch_name when
   biarch64archs +=

`Make' will add a space before it, which makes some mistake when
recognize arch_name.

-- 
YunQiang Su

diff --git a/debian/rules.defs b/debian/rules.defs
index 3941829..b872fa0 100644
--- a/debian/rules.defs
+++ b/debian/rules.defs
@@ -1655,9 +1655,9 @@ biarch32archs := /amd64/ppc64/kfreebsd-amd64/s390x/sparc64/x32/mipsn32/mipsn32el
 biarch64archs := /i386/powerpc/sparc/s390/mips/mipsel/mipsn32/mipsn32el/
 biarchn32archs := /mips/mipsel/mips64/mips64el/
 ifeq (yes,$(MIPS_R6_ENABLED))
-  biarch32archs += mipsn32r6/mipsn32r6el/mips64r6/mips64r6el/
-  biarch64archs += mipsr6/mipsr6el/mipsn32r6/mipsn32r6el/x32/
-  biarchn32archs += mipsr6/mipsr6el/mips64r6/mips64r6el/
+  biarch32archs += /mipsn32r6/mipsn32r6el/mips64r6/mips64r6el/
+  biarch64archs += /mipsr6/mipsr6el/mipsn32r6/mipsn32r6el/x32/
+  biarchn32archs += /mipsr6/mipsr6el/mips64r6/mips64r6el/
 endif
 
 ifeq ($(derivative),Ubuntu)