Makefile.common: obtain HOSTAR via configure.sh just like HOSTCC

$(HOSTAR) may be prefixed just as well as $(HOSTCC) which can be made
configurable easily. Currently it is required to pass this value in as
an argument to make explicitly.

Makefile.common

@@ -60,7 +60,7 @@ HOSTCFLAGS := -fstack-protector-strong -Wall -Werror -std=c11 -O2 -g
 HOSTCPPFLAGS := -I$(TOPDIR)/include
 HOSTLDFLAGS :=
 HOSTLDLIBS :=
-HOSTAR := ar
+HOSTAR := $(CONFIG_HOST_AR)
 
 define HOSTCOMPILE.c
 	@echo "HOSTCC $@"

configure.sh

@@ -57,7 +57,8 @@ Options:
 
 Environment variables affecting the build system configuration:
     HOST_CC
-        C compiler used for host tools and tenders.
+    HOST_AR
+        C compiler and ar tool used for host tools and tenders.
 
     TARGET_CC
     TARGET_LD
@@ -247,6 +248,8 @@ done
 #
 # Configure host tools and tenders based on HOST_CC.
 #
+HOST_AR=${HOST_AR:-ar}
+
 HOST_CC=${HOST_CC:-cc}
 HOST_CC_MACHINE=$(${HOST_CC} -dumpmachine)
 [ $? -ne 0 ] &&
@@ -342,6 +345,7 @@ CONFIG_DISABLE_TOOLCHAIN=1
 CONFIG_HOST_ARCH=${CONFIG_HOST_ARCH}
 CONFIG_HOST=${CONFIG_HOST}
 CONFIG_HOST_CC=${HOST_CC}
+CONFIG_HOST_AR=${HOST_AR}
 CONFIG_HVT_TENDER_ENABLE_CAPSICUM=${CONFIG_HVT_TENDER_ENABLE_CAPSICUM}
 CONFIG_HVT_TENDER=${CONFIG_HVT_TENDER}
 CONFIG_SPT_TENDER=${CONFIG_SPT_TENDER}
@@ -520,6 +524,7 @@ CONFIG_PREFIX=${OPT_PREFIX}
 CONFIG_HOST_ARCH=${CONFIG_HOST_ARCH}
 CONFIG_HOST=${CONFIG_HOST}
 CONFIG_HOST_CC=${HOST_CC}
+CONFIG_HOST_AR=${HOST_AR}
 CONFIG_HVT=${CONFIG_HVT}
 CONFIG_HVT_TENDER_ENABLE_CAPSICUM=${CONFIG_HVT_TENDER_ENABLE_CAPSICUM}
 CONFIG_HVT_TENDER=${CONFIG_HVT_TENDER}