First pass at LLD support for Emscripten (#1346)

* Skeleton of a beginning of o2wasm, WIP and probably not going to be used

* Get building post-cherry-pick

* ast->ir, remove commented out code, include a debug module print because linking

* Read linking section, print emscripten metadata json

* WasmBinaryWriter emits user sections on Module

* Remove debugging prints, everything that isn't needed to build metadata

* Rename o2wasm to lld-metadata

* lld-metadata support for outputting to file

* Use tables index instead of function index for initializer functions

* Add lld-emscripten tool to add emscripten-runtime functions to wasm modules (built with lld)

* Handle EM_ASM in lld-emscripten

* Add a list of functions to forcibly export (for initializer functions)

* Disable incorrect initializer function reading

* Add error printing when parsing .o files in lld-metadata

* Remove ';; METADATA: ' prefix from lld-metadata, output is now standalone json

* Support em_asm consts that aren't at the start of a segment

* Initial test framework for lld-metadata tool

* Add em_asm test

* Add support for WASM_INIT_FUNCS in the linking section

* Remove reloc section parsing because it's unused

* lld-emscripten can read and write text

* Add test harness for lld-emscripten

* Export all functions for now

* Add missing lld test output

* Add support for reading object files differently

Only difference so far is in importing mutable globals being an object
file representation for symbols, but invalid wasm.

* Update help strings

* Update linking tests for stackAlloc fix

* Rename lld-emscripten,lld-metadata to wasm-emscripten-finalize,wasm-link-metadata

* Add help text to header comments

* auto& instead of auto &

* Extract LinkType to abi/wasm-object.h

* Remove special handling for wasm object file reading, allow mutable globals

* Add braces around default switch case

* Fix flake8 errors

* Handle generating dyncall thunks for imports as well

* Use explicit bool for stackPointerGlobal

* Use glob patterns for lld file iteration

* Use __wasm_call_ctors for all initializer functions

1 files changed, 15 insertions, 0 deletions

diff --git a/test/lld/init.c b/test/lld/init.c
new file mode 100644
index 000000000..3a9311e3c
--- /dev/null
+++ b/test/lld/init.c
@@ -0,0 +1,15 @@
+volatile int x, y;
+
+__attribute__((constructor))
+void init_x() {
+    x = 14;
+}
+
+__attribute__((constructor))
+void init_y() {
+    y = 144;
+}
+
+int main() {
+    return x + y;
+}