run go build on all modules to catch compilation errors (#250)

golangci-lint just issues an unreadable warning and quits with a
successful exit status on compilation error. just run a round of go
build ./... to catch those as hard errors.

Makefile

@@ -32,6 +32,10 @@ $(TOOLS_DIR)/stringer: go.mod go.sum tools.go
 precommit: $(TOOLS_DIR)/golangci-lint  $(TOOLS_DIR)/misspell $(TOOLS_DIR)/stringer
 	PATH="$(abspath $(TOOLS_DIR)):$${PATH}" go generate ./...
 	# TODO: Fix this on windows.
+	set -e; for dir in $(ALL_GO_MOD_DIRS); do \
+	  echo "compiling all packages in $${dir}"; \
+	  (cd "$${dir}" && go build ./...); \
+	done
 	set -e; for dir in $(ALL_GO_MOD_DIRS); do \
 	  echo "golangci-lint in $${dir}"; \
 	  (cd "$${dir}" && $(abspath $(TOOLS_DIR))/golangci-lint run --fix); \