fix shared library build with llvm-19 (#526)

Makefile

@@ -617,9 +617,21 @@ PIC_OBJS = \
 # link that using `--whole-archive` rather than pass the object files directly
 # to CC.  This is a workaround for a Windows command line size limitation.  See
 # the `%.a` rule below for details.
-$(SYSROOT_LIB)/%.so: $(OBJDIR)/%.so.a $(BUILTINS_LIB)
-	$(CC) --target=$(TARGET_TRIPLE) -nodefaultlibs -shared --sysroot=$(SYSROOT) \
-	-o $@ -Wl,--whole-archive $< -Wl,--no-whole-archive $(BUILTINS_LIB)
+
+# Note: libc.so is special because it shouldn't link to libc.so.
+# Note: --allow-undefined-file=linker-provided-symbols.txt is
+# a workaround for https://github.com/llvm/llvm-project/issues/103592
+$(SYSROOT_LIB)/libc.so: $(OBJDIR)/libc.so.a $(BUILTINS_LIB)
+	$(CC) $(EXTRA_CFLAGS) --target=${TARGET_TRIPLE} -nodefaultlibs \
+	-shared --sysroot=$(SYSROOT) \
+	-o $@ -Wl,--whole-archive $< -Wl,--no-whole-archive $(BUILTINS_LIB) \
+	-Wl,--allow-undefined-file=linker-provided-symbols.txt
+
+$(SYSROOT_LIB)/%.so: $(OBJDIR)/%.so.a $(SYSROOT_LIB)/libc.so
+	$(CC) $(EXTRA_CFLAGS) --target=${TARGET_TRIPLE} \
+	-shared --sysroot=$(SYSROOT) \
+	-o $@ -Wl,--whole-archive $< -Wl,--no-whole-archive \
+	-Wl,--allow-undefined-file=linker-provided-symbols.txt
 
 $(OBJDIR)/libc.so.a: $(LIBC_SO_OBJS) $(MUSL_PRINTSCAN_LONG_DOUBLE_SO_OBJS)
 

libc-top-half/musl/src/signal/psignal.c

@@ -3,6 +3,13 @@
 #include <signal.h>
 #include <errno.h>
 
+#ifndef __wasilibc_unmodified_upstream
+/* undef the macro to use the standard stderr instead of __stderr_FILE
+ * (the libc internal symbol) as this lives in a separate library,
+ * libwasi-emulated-signal.so. */
+#undef stderr
+#endif
+
 void psignal(int sig, const char *msg)
 {
 	FILE *f = stderr;

linker-provided-symbols.txt

@@ -0,0 +1,3 @@
+__heap_base
+__heap_end
+__c_longjmp