Wasm.mk: disable by default

Fixes partly: #2046

Also, this fixes warnings like:
```
spacetanuki% ./tools/configure.sh -E sim:wamr
  Copy files
  Select CONFIG_HOST_MACOS=y
  Refreshing...
/usr/local/bin/bash: line 1: /bin/clang: No such file or directory
/usr/local/bin/bash: line 1: /bin/clang: No such file or directory              /usr/local/bin/bash: line 1: /bin/clang: No such file or directory
/usr/local/bin/bash: line 1: /bin/clang: No such file or directory
/usr/local/bin/bash: line 1: /bin/clang: No such file or directory
/usr/local/bin/bash: line 1: /bin/clang: No such file or directory
/usr/local/bin/bash: line 1: /bin/clang: No such file or directory
/usr/local/bin/bash: line 1: /bin/clang: No such file or directory
/usr/local/bin/bash: line 1: /bin/clang: No such file or directory
CP: arch/dummy/Kconfig to /Users/yamamoto/git/nuttx/nuttx/arch/dummy/dummy_kconf
ig
CP: boards/dummy/Kconfig to /Users/yamamoto/git/nuttx/nuttx/boards/dummy/dummy_k
config
/usr/local/bin/bash: line 1: /bin/clang: No such file or directory
/usr/local/bin/bash: line 1: /bin/clang: No such file or directory
/usr/local/bin/bash: line 1: /bin/clang: No such file or directory
/usr/local/bin/bash: line 1: /bin/clang: No such file or directory
/usr/local/bin/bash: line 1: /bin/clang: No such file or directory
/usr/local/bin/bash: line 1: /bin/clang: No such file or directory

```

Author: yamt

interpreters/wamr/Kconfig

@@ -75,6 +75,11 @@ config INTERPRETERS_WAMR_LIBC_BUILTIN
 	bool "Enable built-in libc"
 	default n
 
+config INTERPRETERS_WAMR_BUILD_MODULES_FOR_NUTTX
+	bool "Build WASM modules for NuttX system interface (Experimental)"
+	default n
+	depends on INTERPRETERS_WAMR_LIBC_BUILTIN
+
 config INTERPRETERS_WAMR_LIBC_WASI
 	bool "Enable WASI libc"
 	select PSEUDOFS_SOFTLINKS

tools/Wasm.mk

@@ -19,9 +19,8 @@
 #
 ############################################################################
 
-# Only build wasm if one of the following runtime is enabled
 
-ifneq ($(CONFIG_INTERPRETERS_WAMR)$(CONFIG_INTERPRETERS_WASM)$(CONFIG_INTERPRETERS_TOYWASM),)
+ifeq ($(CONFIG_INTERPRETERS_WAMR_BUILD_MODULES_FOR_NUTTX),y)
 include $(APPDIR)$(DELIM)tools$(DELIM)WASI-SDK.defs
 include $(APPDIR)$(DELIM)interpreters$(DELIM)wamr$(DELIM)Toolchain.defs
 
@@ -113,4 +112,4 @@ clean::
 
 endif # WASM_BUILD
 
-endif # CONFIG_INTERPRETERS_WAMR || CONFIG_INTERPRETERS_WASM || CONFIG_INTERPRETERS_TOYWASM
+endif