add preview2_component_type.o to libc.a and libc.so (#472)

This file adds a custom section to each core module linked with wasi-libc.  That
custom section contains component type information needed by e.g. `wasm-tools
component new` to generate a component from the module.  It will be required
once we start using any part of WASI 0.2.0 directly (vs. via a Preview 1
adapter).  In addition, it allows developers to `#include <wasi/preview2.h>` in
their code and make use of those APIs directly even if wasi-libc is not using
them yet.

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

Makefile

@@ -380,6 +380,9 @@ DLMALLOC_OBJS = $(call objs,$(DLMALLOC_SOURCES))
 EMMALLOC_OBJS = $(call objs,$(EMMALLOC_SOURCES))
 LIBC_BOTTOM_HALF_ALL_OBJS = $(call objs,$(LIBC_BOTTOM_HALF_ALL_SOURCES))
 LIBC_TOP_HALF_ALL_OBJS = $(call asmobjs,$(call objs,$(LIBC_TOP_HALF_ALL_SOURCES)))
+ifeq ($(WASI_SNAPSHOT), preview2)
+LIBC_OBJS += $(OBJDIR)/preview2_component_type.o
+endif
 ifeq ($(MALLOC_IMPL),dlmalloc)
 LIBC_OBJS += $(DLMALLOC_OBJS)
 else ifeq ($(MALLOC_IMPL),emmalloc)
@@ -601,6 +604,10 @@ $(OBJDIR)/%.long-double.pic.o: %.c include_dirs
 	@mkdir -p "$(@D)"
 	$(CC) $(CFLAGS) -MD -MP -o $@ -c $<
 
+$(OBJDIR)/preview2_component_type.pic.o $(OBJDIR)/preview2_component_type.o: $(LIBC_BOTTOM_HALF_SOURCES)/preview2_component_type.o
+	@mkdir -p "$(@D)"
+	cp $< $@
+
 $(OBJDIR)/%.pic.o: %.c include_dirs
 	@mkdir -p "$(@D)"
 	$(CC) $(CFLAGS) -MD -MP -o $@ -c $<

expected/wasm32-wasi-preview2/defined-symbols.txt

@@ -19,6 +19,7 @@ __c_locale
 __clock
 __clock_gettime
 __clock_nanosleep
+__component_type_object_force_link_preview2
 __component_type_object_force_link_preview2_public_use_in_this_compilation_unit
 __cos
 __cosdf

expected/wasm32-wasi-preview2/undefined-symbols.txt

@@ -1,5 +1,4 @@
 __addtf3
-__component_type_object_force_link_preview2
 __divtf3
 __eqtf2
 __extenddftf2