Add vlibc scaffold, build system, and documentation

Establish the repository layout per Vox guidelines (layouts/C.md,
building/C.md): Autotools build (GCC-only, C23), five compatibility
profiles (--enable-onlyposix/--enable-muslmimic/--enable-muslext/
--enable-spoof, default vlibc), alongside/overwrite install methods,
vlibc-gcc/vlibc-clang drivers, static-linking requirement (except
spoof), benchmark harness, and tooling (.clang-format/.clang-tidy/
.clangd + compile_commands.json).

compile_commands.json

@@ -0,0 +1,57 @@
+[
+  {
+    "file": "bench_vlibc.c",
+    "arguments": [
+      "/usr/sbin/gcc",
+      "-DHAVE_CONFIG_H",
+      "-I.",
+      "-I..",
+      "-I../include",
+      "-std=c23",
+      "-Wall",
+      "-Wextra",
+      "-g",
+      "-O2",
+      "-MT",
+      "bench_vlibc.o",
+      "-MD",
+      "-MP",
+      "-MF",
+      ".deps/bench_vlibc.Tpo",
+      "-c",
+      "-o",
+      "bench_vlibc.o",
+      "bench_vlibc.c"
+    ],
+    "directory": "/home/specter/vox/vlibc/benchmarks",
+    "output": "bench_vlibc.o"
+  },
+  {
+    "file": "src/vlibc.c",
+    "arguments": [
+      "/usr/sbin/gcc",
+      "-DHAVE_CONFIG_H",
+      "-I.",
+      "-I./include",
+      "-std=c23",
+      "-Wall",
+      "-Wextra",
+      "-g",
+      "-O2",
+      "-MT",
+      "src/vlibc.lo",
+      "-MD",
+      "-MP",
+      "-MF",
+      "src/.deps/vlibc.Tpo",
+      "-c",
+      "src/vlibc.c",
+      "-fPIC",
+      "-DPIC",
+      "-o",
+      "src/.libs/vlibc.o"
+    ],
+    "directory": "/home/specter/vox/vlibc",
+    "output": "src/.libs/vlibc.o"
+  }
+]