Fix C++ exceptions. Add script to build llvm. Support newer meson

cmake/zephyr/Kconfig

@@ -25,5 +25,5 @@ config PICOLIBC_DEFAULT
 	  Zephyr SDK >=0.17.1 always uses Picolibc
 
 choice COMPILER_OPTIMIZATIONS
-	default SPEED_OPTIMIZATIONS if "$(ZEPHYR_TOOLCHAIN_VARIANT)" = "zephyr" && CPP_EXCEPTIONS
+	default SPEED_OPTIMIZATIONS if ("$(ZEPHYR_TOOLCHAIN_VARIANT)" = "zephyr" || "$(ZEPHYR_TOOLCHAIN_VARIANT)" = "zephyr-gnu") && CPP_EXCEPTIONS
 endchoice

contrib/linux_build_llvm.sh

@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+
+# Script to mimic how CI is building llvm toolchain.
+
+# Default is to use current directory as the working directory.
+# SDK is under ${WORKING_ROOT_DIR}/sdk-ng/
+# Build directory is ${WORKING_ROOT_DIR}/build-workspace/
+WORKING_ROOT_DIR="${PWD}"
+SDK_DIR="${WORKING_ROOT_DIR}/sdk-ng"
+BUILD_DIR="${WORKING_ROOT_DIR}/build-workspace"
+
+pushd "${BUILD_DIR}"
+mkdir -p llvm-build
+mkdir -p llvm
+
+#TEST=echo
+cd llvm-build
+$TEST cmake \
+    -GNinja \
+    --install-prefix="${BUILD_DIR}"/llvm \
+    -DLLVM_ENABLE_ZSTD=OFF \
+    ${LLVM_CMAKE_ARGS} \
+    "${SDK_DIR}"/scripts/llvm || exit 1
+
+# Build LLVM toolchain
+$TEST ninja llvm-toolchain || exit 1
+
+# Run LLVM tests
+$TEST ninja check-llvm-toolchain || exit 1
+
+# Install LLVM toolchain
+$TEST ninja install-llvm-toolchain || exit 1
+popd

scripts/llvm/test-support/run-picolibc-tests.py

@@ -66,6 +66,18 @@ def run_tests(meson_command, source_dir, build_dir, variant):
         check=True,
     )
 
+    # Newer meson doesn't apply new configuration with the above
+    # operation, so *also* run a regular configure step
+    subprocess.run(
+        [
+            meson_command,
+            "configure",
+            "-Dtests=true",
+        ],
+        cwd=build_dir,
+        check=True,
+    )
+
     returncode = subprocess.run(
         [meson_command, "test", "-t", "20"],
         cwd=build_dir,