[libj6] Move _init_libc to _init_libj6

As part of the move of jsix-specific code from libc to libj6, all the
library initialization is now libj6-specific, so move it all over.

configs/debug.toml

@@ -64,6 +64,7 @@ ccflags = [
     "-mcmodel=large",
     "-D__ELF__",
     "-D__JSIX__",
+    "-D_LIBCPP_HAS_THREAD_API_EXTERNAL",
     "-isystem${source_root}/sysroot/include",
     "-isystem${source_root}/src/libraries/libc/include",
     "--sysroot='${source_root}/sysroot'"
@@ -113,6 +114,7 @@ ccflags = [
     "-mcmodel=large",
     "-D__ELF__",
     "-D__JSIX__",
+    "-D_LIBCPP_HAS_THREAD_API_EXTERNAL",
     "-isystem${source_root}/sysroot/include",
     "-isystem${source_root}/src/libraries/libc/include",
     "--sysroot='${source_root}/sysroot'"

src/libraries/j6/init.cpp

@@ -8,7 +8,7 @@ static struct j6_init_value *__initv = 0;
 j6_handle_t __handle_sys = j6_handle_invalid;
 j6_handle_t __handle_self = j6_handle_invalid;
 
-void
+extern "C" void
 _get_init(size_t *initc, struct j6_init_value **initv)
 {
 	if (!initc)
@@ -19,8 +19,8 @@ _get_init(size_t *initc, struct j6_init_value **initv)
 		*initv = __initv;
 }
 
-void
-_init_libc(uint64_t *rsp)
+extern "C" void
+_init_libj6(uint64_t *rsp)
 {
 	uint64_t argc = *rsp++;
 	rsp += argc;

src/libraries/j6/module.toml

@@ -1,4 +1,4 @@
 name = "j6"
 kind = "lib"
 includes = ["src/libraries/j6/include"]
-sources = ["syscalls.s"]
+sources = ["init.cpp", "syscalls.s"]

src/libraries/libc/arch/x86_64/crt0.s

@@ -1,17 +1,15 @@
 extern main
 extern exit
-extern _init_libc
+extern _init_libj6
 
 global _start:function (_start.end - _start)
 _start:
 	mov rbp, rsp
 	mov rdi, rsp
-
-	call _init_libc
+	call _init_libj6
 
 	pop rdi
 	mov rsi, rsp
-
 	call main
 
 	mov rdi, rax

src/libraries/libc/module.toml

@@ -7,7 +7,6 @@ deps = ["j6"]
 sources = [
 	"arch/x86_64/_Exit.s",
 	"arch/x86_64/crt0.s",
-	"arch/x86_64/init_libc.c",
 	"ctype/isalnum.c",
 	"ctype/isalpha.c",
 	"ctype/isblank.c",