Don't even include signal.h on WASI

Since version 11, wasi-sysroot doesn't ignore it but spits out
an error instead.

azure-pipelines.yml

@@ -16,7 +16,7 @@ jobs:
           curl https://get.wasmer.io -sSfL | sh
         displayName: Install wasmer
       - script: |
-          curl -sL -o - https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-10/wasi-sdk-10.0-linux.tar.gz | tar xz -f - -C /opt/
+          curl -sL -o - https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-11/wasi-sdk-11.0-linux.tar.gz | tar xz -f - -C /opt/
           sudo mv /opt/wasi-sdk-* /opt/wasi-sdk
           sudo ln -s /opt/wasi-sdk/share/*sysroot* /opt/wasi-sysroot
         displayName: Install the WASI SDK

src/libsodium/sodium/utils.c

@@ -4,12 +4,15 @@
 #include <assert.h>
 #include <errno.h>
 #include <limits.h>
-#include <signal.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
 
+#ifndef __wasm__
+# include <signal.h>
+#endif
+
 #ifdef HAVE_SYS_MMAN_H
 # include <sys/mman.h>
 #endif

test/default/sodium_utils2.c

@@ -3,7 +3,9 @@
 #include <sys/types.h>
 
 #include <limits.h>
+#ifdef HAVE_CATCHABLE_SEGV
 # include <signal.h>
+#endif
 
 #define TEST_NAME "sodium_utils2"
 #include "cmptest.h"

test/default/sodium_utils3.c

@@ -3,7 +3,9 @@
 #include <sys/types.h>
 
 #include <limits.h>
+#ifdef HAVE_CATCHABLE_SEGV
 # include <signal.h>
+#endif
 
 #define TEST_NAME "sodium_utils3"
 #include "cmptest.h"