Add patch that prevents expat in Poco from causing trouble with WASM

As we build a single statically linked bunary for WASM, we will end up
with just one copy of each function in it. Both LO core and Poco
include expat. Upstream Poco builds one of the expat source files as
C++. That causes trouble as it then isn't compatible with what LO core
wants to call. Or something like that. You get "RuntimeError: null
function or function signature mismatch". (The "signature" concept in
WASM is orthogonal to C++ name mangling.)

Signed-off-by: Tor Lillqvist <tml@collabora.com>
Change-Id: Iacf75ed34eea98611cb6aa6867e460697ea1fc4a

wasm/README

@@ -54,8 +54,8 @@ Then build libzstd:
     podman run -v /data/lo/zstd-1.5.2:/data/lo/zstd-1.5.2:rw --security-opt=label=disable -ti public.ecr.aws/allotropia/libo-builders/wasm /bin/bash -c 'source /home/builder/emsdk/emsdk_env.sh && cd /data/lo/zstd-1.5.2/ && emmake make -j8 lib-nomt ZSTD_NO_ASM=1'
 
 Then build POCO:
-* this requires a patch (currently exists patch for 1.12.4 and untested "devel"
-  branch)
+* this requires two patches (currently exists patch for 1.12.4 and untested "devel"
+  branch) plus renaming one source file (which actually is from expat but Poco includes)
 * note that the header Poco/Platform.h maps EMSCRIPTEN to POCO_OS_LINUX
 * it has both Makefiles and CMake but i couldn't get CMake to use CXXFLAGS to
   disable some Linux-specific code; i tried variations on:
@@ -65,6 +65,8 @@ Then build POCO:
     tar -xjvf ~/Downloads/poco-1.12.4-all.tar.bz2
     cd poco-1.12.4-all
     patch -p1 < $HOME/lo/online/wasm/poco-1.12.4-emscripten.patch
+    mv XML/src/xmlparse.cpp XML/src/xmlparse.c
+    patch < $HOME/lo/online/wasm/poco-no-special-expat-sauce.diff
     podman run -v /data/lo/poco-1.12.4-all:/data/lo/poco-1.12.4-all:rw --security-opt=label=disable -ti public.ecr.aws/allotropia/libo-builders/wasm /bin/bash -c 'source /home/builder/emsdk/emsdk_env.sh && cd /data/lo/poco-1.12.4-all && emconfigure ./configure --static --no-samples --no-tests --omit=Crypto,NetSSL_OpenSSL,JWT,Data,Data/SQLite,Data/ODBC,Data/MySQL,Data/PostgreSQL,Zip,PageCompiler,PageCompiler/File2Page,MongoDB,Redis,ActiveRecord,ActiveRecord/Compiler,Prometheus && emmake make -j8 CC=/home/builder/emsdk/upstream/emscripten/emcc CXX=/home/builder/emsdk/upstream/emscripten/em++ LD=/home/builder/emsdk/upstream/emscripten/em++ CXXFLAGS="-DPOCO_NO_LINUX_IF_PACKET_H -pthread -s USE_PTHREADS=1 -s DISABLE_EXCEPTION_CATCHING=0" && make -j8 install INSTALLDIR=/data/lo/poco-1.12.4-all/install'
 
 == Build Online with manually built dependencies ==

wasm/poco-no-special-expat-sauce.diff

@@ -0,0 +1,54 @@
+--- /tmp/poco-poco-1.12.4-release/XML/src/xmlparse.cpp	2022-10-31 19:41:19.000000000 +0200
++++ XML/src/xmlparse.c	2022-12-14 12:50:31.845361409 +0200
+@@ -84,10 +84,7 @@
+ 
+ #define EXPAT_POCO 1
+ 
+-#if defined(EXPAT_POCO)
+-#  include "Poco/RandomStream.h"
+-#  include "Poco/BinaryReader.h"
+-#elif defined(_WIN32)
++#ifdef _WIN32
+ #  define getpid GetCurrentProcessId
+ #else
+ #  include <sys/time.h>  /* gettimeofday() */
+@@ -746,8 +743,6 @@
+        '\0'};
+ 
+ 
+-#if ! defined(EXPAT_POCO)
+-
+ /* To avoid warnings about unused functions: */
+ #if ! defined(HAVE_ARC4RANDOM_BUF) && ! defined(HAVE_ARC4RANDOM)
+ 
+@@ -901,8 +896,6 @@
+ 
+ #endif /* ! defined(HAVE_ARC4RANDOM_BUF) && ! defined(HAVE_ARC4RANDOM) */
+ 
+-#endif /* ! defined(EXPAT_POCO) */
+-
+ static unsigned long
+ ENTROPY_DEBUG(const char *label, unsigned long entropy) {
+   if (getDebugLevel("EXPAT_ENTROPY_DEBUG", 0) >= 1u) {
+@@ -916,12 +909,7 @@
+ generate_hash_secret_salt(XML_Parser parser) {
+   unsigned long entropy;
+   (void)parser;
+-#if defined(EXPAT_POCO)
+-  Poco::RandomInputStream rstr;
+-  Poco::BinaryReader rrdr(rstr);
+-  rrdr >> entropy;
+-  return ENTROPY_DEBUG("RandomInputStream", entropy);
+-#else
++
+   /* "Failproof" high quality providers: */
+ #if defined(HAVE_ARC4RANDOM_BUF)
+   arc4random_buf(&entropy, sizeof(entropy));
+@@ -958,7 +946,6 @@
+                          entropy * (unsigned long)2305843009213693951ULL);
+   }
+ #endif
+-#endif /* defined(EXPAT_POCO) */
+ }
+ 
+ static unsigned long