Set up m2ctx for decomp.me context generation

tools/m2ctx/README.md

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+# Generate a context file for decomp.me
+
+[Decomp.me](https://decomp.me) requires a context file declaring any imported typedefs, structs, or constants that will be used in the decompiled function.
+`m2ctx` generates this context file automatically.
+
+## How to use
+
+Before using `m2ctx`, follow the [installation instructions](../../INSTALL.md) to make a vanilla copy of the game.
+This generates some header files that may be included in decompiled files.
+
+In this example, you are decompiling an asm file `asm/npc_trade.s` into a new C file `src/npc_trade.c`.
+You've created the source file and may have added some imports you know you'll need.
+Your file may look like this:
+
+```
+#include "pokemon.h"
+```
+
+Run `./tools/m2ctx/m2ctx.sh src/npc_trade.c` to generate a context file, which will be output as `ctx.c`.
+Copy the contents of `ctx.c` into the "Context" section of the scratch.
+
+### Adding imports
+
+As you continue decompiling, you may realize that you need to add imports to your source file:
+```diff
+#include "pokemon.h"
++#include "party.h"
+```
+
+You can use `m2ctx` to generate an updated context file which will include declarations from the new imports.
+Simply re-run the command to generate a new context file: `./tools/m2ctx/m2ctx.sh src/npc_trade.c`.

tools/m2ctx/m2ctx.sh

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+#!/usr/bin/env bash
+
+OUT_FILE=ctx.c
+
+GCC=gcc
+FLAGS="-E -P -dD -undef"
+INCLUDES="-Itools/cw/include -Isubprojects/NitroSDK-4.2.30001/include -Ibuild/subprojects/NitroSDK-4.2.30001/gen -Isubprojects/NitroSystem-071126.1/include -Isubprojects/NitroWiFi-2.1.30003/include -Isubprojects/NitroDWC-2.2.30008/include -Isubprojects/libvct-1.3.1/include -Isubprojects/libcrypto/include -Isubprojects/ppwlobby/include -Iinclude -Iasm -Ires -Ilib/gds/include -Ilib/spl/include -Ibuild -Ibuild/res/text -include pch/global_pch.h"
+DEFINES="-DGAME_VERSION=PLATINUM -DGAME_LANGUAGE=ENGLISH -DPM_KEEP_ASSERTS -D_NITRO -DLINK_PPWLOBBY -DNNS_FINALROM -DSDK_4M -DSDK_ARM9 -DSDK_CODE_ARM -DSDK_CW -DSDK_CW_FORCE_EXPORT_SUPPORT -DSDK_FINALROM -DSDK_TS"
+
+generate-ctx () {
+    # Remove any line containing a predefined macro. If not removed, mwccarm
+    # generates compiler warnings.
+    grep "^#include " "$1" | $GCC $FLAGS $INCLUDES $DEFINES  -x c - | sed '/__STDC__\|__STDC_VERSION__\|__STDC_VERSION__\|__STDC_HOSTED__/d' > $OUT_FILE
+}
+
+usage () {
+    echo "Generate a context file for decomp.me."
+    echo "Usage: $0 [-h] [FILEPATH]"
+    echo ""
+    echo "Arguments:"
+    echo "  FILEPATH      Source file used to generate ctx.c"
+    echo ""
+    echo "Options:"
+    echo "  -h            Show this message and exit"
+}
+
+while [[ $# -gt 0 ]]; do
+  key="$1"
+  case $key in
+  -h)
+    usage
+    exit 0
+    ;;
+  *)
+    generate-ctx "$1"
+    exit 0
+    ;;
+  esac
+done