[browser][wasm] Fix provision-wasm build error (#49863)

```
cd emsdk && ./emsdk install `cat emscripten-version.txt`
cat: emscripten-version.txt: No such file or directory
```

diff --git a/src/mono/wasm/Makefile b/src/mono/wasm/Makefile
index 7c04d91..4777abf 100644 (file)
--- a/src/mono/wasm/Makefile
+++ b/src/mono/wasm/Makefile
@@ -33,7 +33,7 @@ all: build-native icu-files source-files header-files
 #  If EMSDK_PATH is not set by the caller, download and setup a local emsdk install.
 #
 
-EMSCRIPTEN_VERSION=`cat emscripten-version.txt`
+EMSCRIPTEN_VERSION := $(shell cat $(TOP)/src/mono/wasm/emscripten-version.txt)
 EMSDK_LOCAL_PATH=emsdk
 EMCC=source $(EMSDK_PATH)/emsdk_env.sh 2>/dev/null && emcc