[scripts] Make j6libc.py into the codegen package

j6libc.py was initially made for libc to generate stdint.h, but it
gained a few things that aren't libc-specific. Move it to a package and
split the int-types-specific code into codegen.int_types.

scripts/codegen/__init__.py

@@ -0,0 +1,16 @@
+import cog
+
+supported_architectures = {
+    "amd64": "__amd64__",
+}
+
+def arch_includes(header, root=""):
+    prefix = "if"
+    for arch, define in supported_architectures.items():
+        cog.outl(f"#{prefix} defined({define})")
+        cog.outl(f"#include <{root}arch/{arch}/{header}>")
+        prefix = "elif"
+    cog.outl("#else")
+    cog.outl('#error "Unsupported platform"')
+    cog.outl("#endif")
+

scripts/codegen/int_types.py

@@ -0,0 +1,43 @@
+import cog
+
+int_widths = (8, 16, 32, 64)
+int_mods = ("fast", "least")
+
+int_types = {
+    # type: abbrev
+    "char": "char",
+    "short": "short",
+    "int": "int",
+    "long": "long",
+    "long long": "llong",
+}
+
+def definition(kind, name, val, width=24):
+    cog.outl(f"{kind} {name:{width}} {val}")
+
+
+atomic_types = {
+    "_Bool": "bool",
+    "signed char": "schar",
+    "char16_t": "char16_t",
+    "char32_t": "char32_t",
+    "wchar_t": "wchar_t",
+    "wchar_t": "wchar_t",
+    "size_t": "size_t",
+    "ptrdiff_t": "ptrdiff_t",
+    "intptr_t": "intptr_t",
+    "uintptr_t": "uintptr_t",
+    "intmax_t": "intmax_t",
+    "uintmax_t": "uintmax_t",
+    }
+
+for name, abbrev in int_types.items():
+    atomic_types.update({name: abbrev, f"unsigned {name}": f"u{abbrev}"})
+
+for width in int_widths:
+    atomic_types.update({t: t for t in (
+            f"int_least{width}_t",
+            f"uint_least{width}_t",
+            f"int_fast{width}_t",
+            f"uint_fast{width}_t")})
+