Add cross-compilation infrastructure support

This commit enhances cross-compilation support with key improvements:
1. Kconfig Toolchain Configuration Menu (configs/Kconfig):
   - Automatic compiler detection using Python scripts
   - Cross-compile prefix detection and validation
   - Supports GCC, Clang, Emscripten, and bare-metal toolchains
2. Cross-platform Endianness Detection
   - Priority-based header inclusion:
     * Bare-metal: Compiler macros (__BYTE_ORDER__)
     * Fallback: Assume little-endian
   - Ensures correct byte order handling across diverse target platforms
3. 128-bit Arithmetic Fallback:
   - Software implementation for 64-bit fixed-point math on 32-bit
   - Targets: RISC-V 32, Arm32, i386 (without __int128_t support)

Author: jserv

configs/Kconfig

@@ -4,6 +4,47 @@ config CONFIGURED
     bool
     default y
 
+menu "Toolchain Configuration"
+
+# Compiler detection using scripts/detect-compiler.py
+config COMPILER_TYPE
+    string
+    default "$(shell,python3 scripts/detect-compiler.py --type 2>/dev/null || echo Unknown)"
+
+config CC_IS_EMCC
+    def_bool $(shell,python3 scripts/detect-compiler.py --is Emscripten 2>/dev/null && echo y || echo n)
+
+config CC_IS_CLANG
+    def_bool $(shell,python3 scripts/detect-compiler.py --is Clang 2>/dev/null && echo y || echo n)
+
+config CC_IS_GCC
+    def_bool $(shell,python3 scripts/detect-compiler.py --is GCC 2>/dev/null && echo y || echo n)
+
+# Cross-compilation support detection
+config CROSS_COMPILE_ENABLED
+    def_bool $(shell,test -n "$(CROSS_COMPILE)" && echo y || echo n)
+
+config CROSS_COMPILE_PREFIX
+    string
+    default "$(CROSS_COMPILE)"
+
+# Verify cross-compilation tools exist
+config CROSS_COMPILE_VALID
+    def_bool $(shell,test -n "$(CROSS_COMPILE)" && which "$(CROSS_COMPILE)gcc" >/dev/null 2>&1 && echo y || echo n)
+
+comment "Toolchain Information"
+
+comment "Cross-compilation: ENABLED"
+    depends on CROSS_COMPILE_ENABLED && CROSS_COMPILE_VALID
+
+comment "Cross-compilation: ENABLED (WARNING: Compiler not found!)"
+    depends on CROSS_COMPILE_ENABLED && !CROSS_COMPILE_VALID
+
+comment "Cross-compilation: DISABLED (Native build)"
+    depends on !CROSS_COMPILE_ENABLED
+
+endmenu
+
 # Dependency detection using Kconfiglib shell function
 config HAVE_SDL2
     def_bool $(shell,pkg-config --exists sdl2 && echo y || echo n)

src/draw-builtin.c

@@ -7,10 +7,35 @@
 
 #include <stdlib.h>
 
-#if defined(__APPLE__)
+/* Cross-platform endianness detection
+ *
+ * Priority:
+ * 1. Linux/glibc: <endian.h>
+ * 2. macOS/BSD: <machine/endian.h>
+ * 3. Bare-metal/embedded: Manual detection via compiler macros
+ *
+ * Note: We don't actually use any endian.h macros in this file currently,
+ * but keep the includes for future compatibility.
+ */
+#if defined(__linux__) || defined(__GLIBC__)
+#include <endian.h>
+#elif defined(__APPLE__) || defined(__FreeBSD__) || defined(__NetBSD__) || \
+    defined(__OpenBSD__)
 #include <machine/endian.h>
+#elif defined(__BYTE_ORDER__)
+/* Compiler-provided endianness (GCC/Clang bare-metal) */
+#define __LITTLE_ENDIAN 1234
+#define __BIG_ENDIAN 4321
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#define __BYTE_ORDER __LITTLE_ENDIAN
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+#define __BYTE_ORDER __BIG_ENDIAN
+#endif
 #else
-#include <endian.h>
+/* Fallback: Assume little-endian (x86, ARM, RISC-V default) */
+#define __LITTLE_ENDIAN 1234
+#define __BIG_ENDIAN 4321
+#define __BYTE_ORDER __LITTLE_ENDIAN
 #endif
 
 #include "twin_private.h"