[libc] Add wasm support for some submodules in llvm-libc. (#154383)

Introducing several emscripten-specific changes to the llvm-libc headers
as well as adding a wasm sigsetjmp.cpp.

libc/src/__support/StringUtil/platform_errors.h

@@ -9,7 +9,7 @@
 #ifndef LLVM_LIBC_SRC___SUPPORT_STRINGUTIL_PLATFORM_ERRORS_H
 #define LLVM_LIBC_SRC___SUPPORT_STRINGUTIL_PLATFORM_ERRORS_H
 
-#if defined(__linux__) || defined(__Fuchsia__)
+#if defined(__linux__) || defined(__Fuchsia__) || defined(__EMSCRIPTEN__)
 #include "tables/linux_platform_errors.h"
 #else
 #include "tables/minimal_platform_errors.h"

libc/src/__support/macros/properties/architectures.h

@@ -41,6 +41,10 @@
 #define LIBC_TARGET_ARCH_IS_ARM
 #endif
 
+#if defined(__wasm__)
+#define LIBC_TARGET_ARCH_IS_WASM
+#endif
+
 #if defined(__aarch64__) || defined(__arm64__) || defined(_M_ARM64)
 #define LIBC_TARGET_ARCH_IS_AARCH64
 #endif

libc/src/setjmp/wasm/sigsetjmp.cpp

@@ -0,0 +1,18 @@
+//===-- Implementation of sigsetjmp ---------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/setjmp/sigsetjmp.h"
+#include "hdr/offsetof_macros.h"
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE_DECL {
+[[gnu::returns_twice]] int sigsetjmp(jmp_buf sigjmp_buf,
+                                     [[maybe_unused]] int savesigs) {
+  return setjmp(sigjmp_buf);
+}
+} // namespace LIBC_NAMESPACE_DECL