Fix build tags with comma on muslc as well

Dockerfile

@@ -1,5 +1,5 @@
-# docker build . -t cosmwasm/wasm:latest
-# docker run --rm -it cosmwasm/wasm:latest /bin/sh
+# docker build . -t cosmwasm/wasmd:latest
+# docker run --rm -it cosmwasm/wasmd:latest /bin/sh
 FROM cosmwasm/go-ext-builder:0.8.2-alpine AS builder
 
 RUN apk add git
@@ -10,6 +10,11 @@ RUN apk add libusb-dev linux-headers
 WORKDIR /code
 COPY . /code
 
+# try this one out
+RUN BUILD_TAGS=muslc make view
+
+RUN false
+
 # download all deps
 RUN go mod download
 # TODO: how to use this instead of hardcoding GO_COSMWASM

Makefile

@@ -40,10 +40,10 @@ endif
 build_tags += $(BUILD_TAGS)
 build_tags := $(strip $(build_tags))
 
-whitespace :=
-whitespace += $(whitespace)
+empty:=
+space:= $(empty) $(empty)
 comma := ,
-build_tags_comma_sep := $(subst $(whitespace),$(comma),$(build_tags))
+build_tags_comma_sep := $(subst $(space),$(comma),$(build_tags))
 
 # process linker flags
 
@@ -60,7 +60,7 @@ endif
 ldflags += $(LDFLAGS)
 ldflags := $(strip $(ldflags))
 
-BUILD_FLAGS := -tags $(build_tags_comma_sep) -ldflags '$(ldflags)' -trimpath
+BUILD_FLAGS := -tags "$(build_tags_comma_sep)" -ldflags '$(ldflags)' -trimpath
 
 # The below include contains the tools target.
 include contrib/devtools/Makefile