Remove glibc compat shim with restrictive license

Unlike the other glibc source code checked into the repo, `csu/init.c`
did not have a license clause that allowed linking without restrictions.

`_IO_stdin_used` is the only symbol in the file and appears to be a 20
year old compatibility shim for the glibc 2.0 ABI. Obsolete in 2.1.

CMakeLists.txt

@@ -835,7 +835,6 @@ set(ZIG_LIBC_FILES
     "glibc/csu/abi-note.S"
     "glibc/csu/abi-tag.h"
     "glibc/csu/elf-init.c"
-    "glibc/csu/init.c"
     "glibc/debug/stack_chk_fail_local.c"
     "glibc/elf/elf.h"
     "glibc/include/alloca.h"

libc/glibc/csu/init.c

@@ -1,23 +0,0 @@
-/* Special startup support.
-   Copyright (C) 1997-2019 Free Software Foundation, Inc.
-   This file is part of the GNU C Library.
-
-   The GNU C Library is free software; you can redistribute it and/or
-   modify it under the terms of the GNU Lesser General Public
-   License as published by the Free Software Foundation; either
-   version 2.1 of the License, or (at your option) any later version.
-
-   The GNU C Library is distributed in the hope that it will be useful,
-   but WITHOUT ANY WARRANTY; without even the implied warranty of
-   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-   Lesser General Public License for more details.
-
-   You should have received a copy of the GNU Lesser General Public
-   License along with the GNU C Library; if not, see
-   <http://www.gnu.org/licenses/>.  */
-
-/* Vestigial libio version number.  Some code in libio checks whether
-   this symbol exists in the executable, but nothing looks at its
-   value anymore; the value it was historically set to has been
-   preserved out of an abundance of caution.  */
-const int _IO_stdin_used = 0x20001;

src/link.cpp

@@ -426,38 +426,13 @@ static const char *get_libc_crt_file(CodeGen *parent, const char *file) {
             c_file->args.append("-g");
             c_file->args.append("-Wa,--noexecstack");
             return build_libc_object(parent, "abi-note", c_file);
-        } else if (strcmp(file, "init.o") == 0) {
-            CFile *c_file = allocate<CFile>(1);
-            c_file->source_path = path_from_libc(parent, "glibc" OS_SEP "csu" OS_SEP "init.c");
-            c_file->args.append("-I");
-            c_file->args.append(path_from_libc(parent, "glibc" OS_SEP "csu"));
-            glibc_add_include_dirs(parent, c_file);
-            c_file->args.append("-std=gnu11");
-            c_file->args.append("-fgnu89-inline");
-            c_file->args.append("-g");
-            c_file->args.append("-O2");
-            c_file->args.append("-fmerge-all-constants");
-            c_file->args.append("-fno-stack-protector");
-            c_file->args.append("-fmath-errno");
-            c_file->args.append("-DSTACK_PROTECTOR_LEVEL=0");
-            c_file->args.append("-ftls-model=initial-exec");
-            c_file->args.append("-D_LIBC_REENTRANT");
-            c_file->args.append("-include");
-            c_file->args.append(path_from_libc(parent, "glibc" OS_SEP "include" OS_SEP "libc-modules.h"));
-            c_file->args.append("-DMODULE_NAME=libc");
-            c_file->args.append("-include");
-            c_file->args.append(path_from_libc(parent, "glibc" OS_SEP "include" OS_SEP "libc-symbols.h"));
-            c_file->args.append("-DTOP_NAMESPACE=glibc");
-            return build_libc_object(parent, "init", c_file);
         } else if (strcmp(file, "Scrt1.o") == 0) {
             const char *start_os = get_libc_crt_file(parent, "start.os");
             const char *abi_note_o = get_libc_crt_file(parent, "abi-note.o");
-            const char *init_o = get_libc_crt_file(parent, "init.o");
             CodeGen *child_gen = create_child_codegen(parent, nullptr, OutTypeObj, nullptr);
             codegen_set_out_name(child_gen, buf_create_from_str("Scrt1"));
             codegen_add_object(child_gen, buf_create_from_str(start_os));
             codegen_add_object(child_gen, buf_create_from_str(abi_note_o));
-            codegen_add_object(child_gen, buf_create_from_str(init_o));
             codegen_build_and_link(child_gen);
             return buf_ptr(&child_gen->output_file_path);
         } else if (strcmp(file, "libc_nonshared.a") == 0) {