[piexwasm] Add Makefile to em++ compile the piex code

Make em++ compile -Os and export needed SDK symbols: cwrap and the SDK
callback helpers addFunction and removeFunction). Compile and link the
PIEX with with piex.cpp, which will be added in a future CL.

Bug: 935285
Change-Id: I1c3ebcf088cb8ece69767b9d26012bc015083615
Reviewed-on: https://chromium-review.googlesource.com/c/1487754Reviewed-by: Anand Mistry <amistry@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Auto-Submit: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635399}

ui/file_manager/image_loader/piex/Makefile

+# Makefile for piex-wasm
+
+PIEX = node_modules/piex
+
+PSRC = $(PIEX)/src/piex.cc \
+       $(PIEX)/src/tiff_parser.cc \
+       $(PIEX)/src/image_type_recognition/image_type_recognition_lite.cc \
+       $(PIEX)/src/tiff_directory/tiff_directory.cc \
+       $(PIEX)/src/binary_parse/range_checked_byte_ptr.cc \
+       $(PIEX)/src/binary_parse/cached_paged_byte_array.cc
+
+WAPI = ["cwrap", "addFunction", "removeFunction"]
+
+INCS = -I $(PIEX) -I .
+WASM = -s WASM=1 -fno-exceptions -D NO_ENABLE_LOGGING
+WOPT = -Os --llvm-opts 3 \
+  -s STRICT=1 \
+  -s ALLOW_MEMORY_GROWTH=1 \
+  -s EXTRA_EXPORTED_RUNTIME_METHODS='$(WAPI)' \
+  -s RESERVED_FUNCTION_POINTERS=2
+
+all: a.out.js
+
+a.out.js: piex.cpp.bc piex.src.bc
+	em++ --bind --std=c++11 $(WASM) $(WOPT) $^
+
+piex.cpp.bc: piex.cpp log.h logfatal.h Makefile
+	em++ --bind --std=c++11 $(WASM) $(WOPT) $(INCS) piex.cpp -o $@
+
+piex.src.bc: $(PSRC) Makefile
+	em++ --bind --std=c++11 $(WASM) $(WOPT) $(INCS) $(PSRC) -o $@
+
+.PHONY: clean
+
+clean:
+	$(shell rm -f tests.hash tests.log package-lock* *.bc a.out.*)