make sysroot relative to have a relocatable gcc

Signed-off-by: Thorsten Glaser <tg@mirbsd.org>

mk/vars.mk

@@ -29,6 +29,9 @@ STAGING_HOST_DIR:=	${BASE_DIR}/host_${CPU_ARCH}_${ADK_TARGET_LIBC}
 STAGING_HOST_DIR_PFX:=	${BASE_DIR}/host_*
 STAGING_TARGET_DIR:=	${BASE_DIR}/target_${CPU_ARCH}_${ADK_TARGET_LIBC}
 STAGING_TARGET_DIR_PFX:=${BASE_DIR}/target_*
+# relation from STAGING_HOST_DIR to STAGING_TARGET_DIR (for gcc to find
+# its sysroot while staying relocatable)
+STAGING_HOST2TARGET:=	../target_${CPU_ARCH}_${ADK_TARGET_LIBC}
 TOOLCHAIN_BUILD_DIR=	$(BASE_DIR)/toolchain_build_${CPU_ARCH}_${ADK_TARGET_LIBC}
 TOOLCHAIN_BUILD_DIR_PFX=$(BASE_DIR)/toolchain_build_*
 TOOLS_BUILD_DIR=	$(BASE_DIR)/tools_build

toolchain/gcc/Makefile

@@ -133,7 +133,7 @@ $(GCC_BUILD_DIR_FINAL)/.configured:
 		$(WRKBUILD)/configure \
 			${GCC_CONFOPTS} \
 			--enable-languages=$(LANGUAGES) \
-			--with-sysroot=$(STAGING_TARGET_DIR) \
+			--with-sysroot='$${prefix}/${STAGING_HOST2TARGET}' \
 			--with-slibdir=$(STAGING_TARGET_DIR)/lib \
 			--enable-shared \
 	);