* Add shell scripts to easily build OpenSSL for use with DM.

BUILD-DM.md

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+# Building OpenSSL
+
+You want to check out Discord Messenger?  Well you're probably going to want to compile OpenSSL,
+so I've provided some shell scripts to make it easier to build.
+
+The main command to run is:
+```
+./buildit
+```
+
+Note: You will need Mingw-w64, and specifically the mingw32 shell.  You'll also need to follow
+the [notes on Windows](NOTES-WINDOWS.md) regarding the packages to install.
+
+### Configure
+
+The script configures OpenSSL to:
+- compile with MinGW
+- not include any assembly blobs (makes it not use advanced instruction sets such as SSE2)
+- defines `WINVER` and `_WIN32_WINNT` as `0x0501` (to avoid OpenSSL targeting Vista+ APIs)
+- defines `OPENSSL_THREADS` to allow OpenSSL to use threads
+- defines `OPENSSL_NO_ASYNC` and `OPENSSL_USE_NODELETE` to avoid OpenSSL importing certain Vista+
+  APIs
+
+### Build
+
+Then, it runs `make -j$(nproc)`. It takes the number of logical processors in your system, and
+runs a make job for each.  This allows a faster build while not totally blowing up your computer
+(as `make -j` would do - unboundedly spawn jobs)
+
+### Patch to remove a single XP+ import
+
+Finally, it runs `./patchlibcrypto`, which compiles a single C file, `./patchlibcrypto.c` to a temp
+file, runs it, and deletes it.  `patchlibcrypto.c` patches libcrypto-3.dll to change imports to
+`_strtoi64` and `_strtoui64` to `iswxdigit` and `isleadbyte` (functions likely to return zero given
+the parameters, and have the same length, and are also exported by msvcrt.dll), by doing a dumb
+binary search.
+
+Note: Ideally I'd remove all uses of \*scanf, though not totally sure that'll remove the import
+patch requirement.
+
+Note: This patch step is optional if you don't intend to run Discord Messenger on Windows 2000 or
+older.
+
+-iProgramInCpp

buildit

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+#!/bin/sh
+# Build script for OpenSSL targeting Windows 2000 (and older).
+
+# run the configure script.
+perl ./Configure mingw no-asm -DWINVER=0x0501 -D_WIN32_WINNT=0x0501 -DOPENSSL_THREADS -DOPENSSL_NO_ASYNC -DOPENSSL_USE_NODELETE
+
+# Make
+make -j$(nproc)
+
+# Patch libcrypto.dll
+./patchlibcrypto

patchlibcrypto

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+#!/bin/sh
+
+# Compile patchlibcrypto.c into a temporary file, run it, and then delete it.
+TEMPFILENAME=$(mktemp)
+echo Compiling patchlibcrypto.c to $TEMPFILENAME.exe
+gcc patchlibcrypto.c -o $TEMPFILENAME.exe
+$TEMPFILENAME.exe
+rm $TEMPFILENAME

patchlibcrypto.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+
+void* find_memory(void* haystack, size_t size_haystack, const void* needle, size_t size_needle)
+{
+	if (size_needle > size_haystack)
+		return NULL;
+
+	char* haystack_ptr = haystack;
+	for (size_t i = 0; i < size_haystack - size_needle + 1; i++) {
+		if (memcmp(haystack_ptr, needle, size_needle) == 0)
+			return haystack_ptr;
+
+		haystack_ptr++;
+	}
+
+	return NULL;
+}
+
+int main()
+{
+	FILE *f = fopen("libcrypto-3.dll", "rb");
+	if (!f) {
+		perror("could not open libcrypto-3.dll");
+		return 1;
+	}
+
+	long size;
+	fseek(f, 0, SEEK_END);
+	size = ftell(f);
+	fseek(f, 0, SEEK_SET);
+
+	if (size < 0) {
+		perror("libcrypto-3.dll is not a file or something");
+		fclose(f);
+		return 1;
+	}
+
+	char* fdata = malloc(size);
+	if (fread(fdata, 1, size, f) != size) {
+		perror("could not read entire file libcrypto-3.dll");
+		fclose(f);
+		return 1;
+	}
+
+	fclose(f);
+
+	char* strtoi64_place = find_memory(fdata, size, "_strtoi64", 9);
+	char* strtoui64_place = find_memory(fdata, size, "_strtoui64", 10);
+
+	if (!strtoi64_place) {
+		fprintf(stderr, "cannot find _strtoi64 in libcrypto-3");
+		return 1;
+	}
+	if (!strtoui64_place) {
+		fprintf(stderr, "cannot find _strtoui64 in libcrypto-3");
+		return 1;
+	}
+
+	memcpy(strtoi64_place, "iswxdigit", 9);
+	memcpy(strtoui64_place, "isleadbyte", 10);
+
+	f = fopen("libcrypto-3-patched.dll", "wb");
+	if (!f) {
+		perror("cannot open libcrypto-3-patched.dll for writing");
+		return 1;
+	}
+
+	if (fwrite(fdata, 1, size, f) != size) {
+		perror("cannot write all bytes to libcrypto-3-patched.dll");
+		fclose(f);
+		return 1;
+	}
+
+	fclose(f);
+
+	// perform the swap
+	if (rename("libcrypto-3.dll", "libcrypto-3-original.dll") < 0) {
+		if (errno == EEXIST) {
+			// delete the file
+			if (remove("libcrypto-3-original.dll") < 0) {
+				perror("couldn't delete old libcrypto-3-original.dll to rename the actual original over");
+				return 1;
+			}
+		}
+		else {
+			perror("cannot rename libcrypto-3.dll to libcrypto-3-original.dll");
+			return 1;
+		}
+	}
+	if (rename("libcrypto-3-patched.dll", "libcrypto-3.dll") < 0) {
+		perror("cannot rename libcrypto-3-patched.dll to libcrypto-3.dll");
+		return 1;
+	}
+
+	return 0;
+}