gh-95205: Improve WASM README.md (GH-95267)

Co-authored-by: Erlend Egeberg Aasland <erlend.aasland@protonmail.com>

Tools/wasm/wasi-env

@@ -0,0 +1,68 @@
+#!/bin/sh
+set -e
+
+# function
+usage() {
+    echo "wasi-env - Run command with WASI-SDK"
+    echo ""
+    echo "wasi-env is a helper to set various environment variables to"
+    echo "run configure and make with WASI-SDK. A WASI-SDK must be either"
+    echo "installed at /opt/wasi-sdk or the env var 'WASI_SDK_PATH' must"
+    echo "set to the root of a WASI-SDK."
+    echo ""
+    echo "Usage: wasi-env command [...]"
+    echo ""
+    echo "    -h --help     display this help and exit"
+    echo ""
+}
+
+case $1 in
+    -h|--help)
+        usage
+        exit
+        ;;
+esac
+
+if test -z "$1"; then
+    echo "ERROR: command required" >&2
+    usage
+    exit 1
+fi
+
+WASI_SDK_PATH="${WASI_SDK_PATH:-/opt/wasi-sdk}"
+
+if ! test -x "${WASI_SDK_PATH}/bin/clang"; then
+    echo "Error: ${WASI_SDK_PATH}/bin/clang does not exist." >&2
+    exit 2
+fi
+
+# --sysroot is required if WASI-SDK is not installed in /opt/wasi-sdk.
+WASI_SYSROOT="${WASI_SDK_PATH}/share/wasi-sysroot"
+CC="${WASI_SDK_PATH}/bin/clang --sysroot=${WASI_SYSROOT}"
+CPP="${WASI_SDK_PATH}/bin/clang-cpp --sysroot=${WASI_SYSROOT}"
+CXX="${WASI_SDK_PATH}/bin/clang++ --sysroot=${WASI_SYSROOT}"
+
+# use ccache if available
+if command -v ccache >/dev/null 2>&1; then
+    CC="ccache ${CC}"
+    CPP="ccache ${CPP}"
+    CXX="ccache ${CXX}"
+fi
+
+LDSHARED="${WASI_SDK_PATH}/bin/wasm-ld"
+AR="${WASI_SDK_PATH}/bin/llvm-ar"
+RANLIB="${WASI_SDK_PATH}/bin/ranlib"
+
+# instruct pkg-config to use sysroot
+PKG_CONFIG_PATH=""
+PKG_CONFIG_LIBDIR="${WASI_SYSROOT}/lib/pkgconfig:${WASI_SYSROOT}/share/pkgconfig"
+PKG_CONFIG_SYSROOT_DIR="${WASI_SYSROOT}"
+
+PATH="${WASI_SDK_PATH}/bin:$PATH"
+
+export WASI_SDK_PATH
+export CC CPP CXX LDSHARED AR RANLIB
+export PKG_CONFIG_PATH PKG_CONFIG_LIBDIR PKG_CONFIG_SYSROOT_DIR
+export PATH
+
+exec "$@"