package/go: Add HOST_GO_CGO_ENABLED

The go compiler's cgo support uses threads.  If BR2_TOOLCHAIN_HAS_THREADS is
set, build in cgo support for any go programs that may need it.  Note that
any target package needing cgo support must include
'depends on BR2_TOOLCHAIN_HAS_THREADS' in its config file.

Fixes build errors like these:

  error: #warning requested reentrant code

  http://autobuild.buildroot.net/results/42a8d07101d8d954511d1c884ecb66e8d861899e

Signed-off-by: Geoff Levand <geoff@infradead.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/go/go.mk

@@ -44,6 +44,16 @@ HOST_GO_TARGET_ENV = \
 	CXX=$(TARGET_CXX) \
 	GOTOOLDIR="$(HOST_GO_TOOLDIR)"
 
+# The go compiler's cgo support uses threads.  If BR2_TOOLCHAIN_HAS_THREADS is
+# set, build in cgo support for any go programs that may need it.  Note that
+# any target package needing cgo support must include
+# 'depends on BR2_TOOLCHAIN_HAS_THREADS' in its config file.
+ifeq (BR2_TOOLCHAIN_HAS_THREADS,y)
+HOST_GO_CGO_ENABLED = 1
+else
+HOST_GO_CGO_ENABLED = 0
+endif
+
 # The go build system doesn't have the notion of cross compiling, but just the
 # notion of architecture.  When the host and target architectures are different
 # it expects to be given a target cross compiler in CC_FOR_TARGET.  When the
@@ -60,7 +70,7 @@ HOST_GO_MAKE_ENV = \
 	GOARCH=$(GO_GOARCH) \
 	$(if $(GO_GOARM),GOARM=$(GO_GOARM)) \
 	GOOS=linux \
-	CGO_ENABLED=1 \
+	CGO_ENABLED=$(HOST_GO_CGO_ENABLED) \
 	CC=$(HOSTCC_NOCCACHE)
 
 HOST_GO_TARGET_CC = \