golang: fix package clean / autoremove, add output whitespace

go 1.11 added modules, which are cached locally. The go developers have
decided to make this cache read-only (golang/go#27455), which causes
problems with package clean / autoremove (#7635).

This adds a call to clear this cache right after building, as currently
there is no easy way to hook into autoremove (it may be possible to hook
into package clean).

This also adds whitespace (blank lines) to certain places in make
output, to aid debugging.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

lang/golang/golang-package.mk

@@ -171,6 +171,7 @@ define GoPackage/Build/Configure
 			mkdir -p $$$$(dirname $$$$dest) ; \
 			$(CP) $$$$file $$$$dest ; \
 		done ; \
+		echo ; \
 		\
 		link_contents() { \
 			local src=$$$$1 ; \
@@ -209,6 +210,7 @@ define GoPackage/Build/Configure
 		else \
 			echo "Not building binaries, skipping symlinks" ; \
 		fi ; \
+		echo ; \
 	)
 endef
 
@@ -224,16 +226,21 @@ define GoPackage/Build/Compile
 			CXX=$(TARGET_CXX) \
 			$(call GoPackage/Environment) ; \
 		\
+		echo "Finding targets" ; \
 		targets=$$$$(go list $(GO_PKG_BUILD_PKG)) ; \
 		for pattern in $(GO_PKG_EXCLUDES); do \
 			targets=$$$$(echo "$$$$targets" | grep -v "$$$$pattern") ; \
 		done ; \
+		echo ; \
 		\
 		if [ "$(GO_PKG_GO_GENERATE)" = 1 ]; then \
+			echo "Calling go generate" ; \
 			go generate -v $(1) $$$$targets ; \
+			echo ; \
 		fi ; \
 		\
 		if [ "$(GO_PKG_SOURCE_ONLY)" != 1 ]; then \
+			echo "Building targets" ; \
 			case $(GO_ARCH) in \
 			arm)             installsuffix="-installsuffix v$(GO_ARM)" ;; \
 			mips|mipsle)     installsuffix="-installsuffix $(GO_MIPS)" ;; \
@@ -250,10 +257,16 @@ define GoPackage/Build/Compile
 				$(1) \
 				$$$$targets ; \
 			retval=$$$$? ; \
+			echo ; \
 			\
 			if [ "$$$$retval" -eq 0 ] && [ -z "$(call GoPackage/has_binaries)" ]; then \
 				echo "No binaries were generated, consider adding GO_PKG_SOURCE_ONLY:=1 to Makefile" ; \
+				echo ; \
 			fi ; \
+			\
+			echo "Cleaning module download cache (golang/go#27455)" ; \
+			go clean -modcache ; \
+			echo ; \
 		fi ; \
 		exit $$$$retval ; \
 	)