clang-cl doesn't define __GNUC__, but does accept the GCC asm barriers.

diff --git a/src/prebuilt/wasm2c_simd_source_declarations.cc b/src/prebuilt/wasm2c_simd_source_declarations.cc
--- a/src/prebuilt/wasm2c_simd_source_declarations.cc
+++ b/src/prebuilt/wasm2c_simd_source_declarations.cc
@@ -4,7 +4,9 @@ R"w2c_template(    WASM_RT_NONCONFORMING_ALLOW_OOB_READ_ELIMINATION
 )w2c_template"
 R"w2c_template(#define SIMD_FORCE_READ(var)
 )w2c_template"
-R"w2c_template(#elif defined(__GNUC__) && WASM_RT_MEMCHECK_GUARD_PAGES
+R"w2c_template(#elif (defined(__GNUC__) || defined(__clang__)) && \
+)w2c_template"
+R"w2c_template(    WASM_RT_MEMCHECK_GUARD_PAGES
 )w2c_template"
 R"w2c_template(#if defined(__x86_64__)
 )w2c_template"
diff --git a/src/prebuilt/wasm2c_source_declarations.cc b/src/prebuilt/wasm2c_source_declarations.cc
--- a/src/prebuilt/wasm2c_source_declarations.cc
+++ b/src/prebuilt/wasm2c_source_declarations.cc
@@ -361,7 +361,9 @@ R"w2c_template(#define FORCE_READ_INT(var)
 )w2c_template"
 R"w2c_template(#define FORCE_READ_FLOAT(var)
 )w2c_template"
-R"w2c_template(#elif defined(__GNUC__) && WASM_RT_MEMCHECK_GUARD_PAGES
+R"w2c_template(#elif (defined(__GNUC__) || defined(__clang__)) && \
+)w2c_template"
+R"w2c_template(    WASM_RT_MEMCHECK_GUARD_PAGES
 )w2c_template"
 R"w2c_template(#define FORCE_READ_INT(var) __asm__("" ::"r"(var))
 )w2c_template"
diff --git a/wasm2c/wasm-rt.h b/wasm2c/wasm-rt.h
--- a/wasm2c/wasm-rt.h
+++ b/wasm2c/wasm-rt.h
@@ -160,8 +160,9 @@ extern "C" {
  * compiler or the embedder must permit a non-conforming setting (allow dead
  * read elimination from linear memory)
  */
-#if UINTPTR_MAX > 0xffffffff && WASM_RT_USE_MMAP && \
-    (WASM_RT_NONCONFORMING_ALLOW_OOB_READ_ELIMINATION || defined(__GNUC__))
+#if UINTPTR_MAX > 0xffffffff && WASM_RT_USE_MMAP &&      \
+    (WASM_RT_NONCONFORMING_ALLOW_OOB_READ_ELIMINATION || \
+     defined(__GNUC__) || defined(__clang__))
 #define WASM_RT_GUARD_PAGES_SUPPORTED 1
 #else
 #define WASM_RT_GUARD_PAGES_SUPPORTED 0