feat: build userspace programs with the x86_64-montauk toolchain

Switch all program and library Makefiles from host g++ (or the
bare-metal x86_64-elf compiler) to x86_64-montauk-g++/gcc and drop the
flags the target now owns: -nostdinc + kernel freestanding -isystem
paths, -m64/-march, -fno-PIC, -mno-red-zone, -mcmodel=small, -static,
-Wl,-m,elf_x86_64, -z max-page-size, --build-id=none. Deliberate
policy flags stay (-ffreestanding, per-app SSE, -nostdlib + link.ld).

Program builds now require the montauk toolchain and fail with a
pointer to build-montauk-toolchain.sh; lib/ and libs/ keep the host
fallback since the toolchain script bootstraps libc through it.
Userspace is also now pinned to the cross GCC instead of drifting
with the distro compiler.

Co-Authored-By: Claude Fable 5 <[email protected]>

programs/GNUmakefile

@@ -6,50 +6,40 @@ MAKEFLAGS += -rR
 ARCH := x86_64
 
 # Auto-detect cross compiler from toolchain/local/.
-TOOLCHAIN_PREFIX := $(shell cd .. && pwd)/toolchain/local/bin/x86_64-elf-
-ifneq ($(wildcard $(TOOLCHAIN_PREFIX)gcc),)
+TOOLCHAIN_PREFIX := $(shell cd .. && pwd)/toolchain/local/bin/x86_64-montauk-
+ifeq ($(wildcard $(TOOLCHAIN_PREFIX)gcc),)
+    CXX = $(error x86_64-montauk toolchain not found. Run ./toolchain/build-montauk-toolchain.sh first)
+    CC = $(error x86_64-montauk toolchain not found. Run ./toolchain/build-montauk-toolchain.sh first)
+else
     CXX := $(TOOLCHAIN_PREFIX)g++
     CC  := $(TOOLCHAIN_PREFIX)gcc
-else
-    CXX := g++
-    CC  := gcc
 endif
 
-# Compiler flags: freestanding, no stdlib, kernel-mode compatible.
+# Compiler flags. The x86_64-montauk toolchain supplies the target ABI
+# (static ET_EXEC, 4 KiB pages, no red zone) and header paths; system
+# programs additionally avoid FP/SIMD and their own runtime (-nostdlib).
 override CXXFLAGS := \
     -std=gnu++20 \
     -g -O2 -pipe \
     -Wall \
     -Wextra \
-    -nostdinc \
     -ffreestanding \
     -fno-stack-protector \
     -fno-stack-check \
-    -fno-PIC \
     -fno-rtti \
     -fno-exceptions \
     -ffunction-sections \
     -fdata-sections \
-    -m64 \
-    -march=x86-64 \
     -mno-80387 \
     -mno-mmx \
     -mno-sse \
     -mno-sse2 \
-    -mno-red-zone \
-    -mcmodel=small \
-    -I include \
-    -isystem ../kernel/freestnd-c-hdrs/x86_64/include \
-    -isystem ../kernel/freestnd-cxx-hdrs/x86_64/include
+    -I include
 
 # Linker flags: freestanding static ELF.
 override LDFLAGS := \
     -nostdlib \
-    -static \
-    -Wl,--build-id=none \
     -Wl,--gc-sections \
-    -Wl,-m,elf_x86_64 \
-    -z max-page-size=0x1000 \
     -T link.ld
 
 # Output directory.