feat: ship native dev tools and target sysroot at 0:/usr

The devkit target in programs/GNUmakefile stages the native binutils
(as, ld, ar, nm, objcopy, objdump, readelf, ranlib, strip, size,
strings, addr2line, c++filt, elfedit as *.elf) into the image at
0:/usr/bin, plus a target-side sysroot: libc headers, montauk/ and
Api/ SDK headers and the freestanding C++ set at 0:/usr/include, and
libc.a + crt1/crti/crtn objects (with empty libm/libstdc++ stand-ins)
at 0:/usr/lib. ld's ldscripts ship under 0:/usr/x86_64-montauk.

The /usr prefix matches the binutils configure prefix, and the kernel
already resolves driveless absolute paths against the cwd drive, so
compiled-in /usr/lib search paths work natively on drive 0.

The shell resolves commands from 0:/usr/bin (after 0:/os) and tab
completion lists it. When toolchain/native/ has not been built, the
devkit step skips cleanly and the image builds as before.

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

programs/src/shell/tabcompletion.cpp

@@ -148,6 +148,36 @@ int get_completions(		// returns no. of results
 		} 
 	}
 
+	// ---- Native dev tools (0:/usr/bin/*.elf) ----
+
+	const char* usr_names[RD_MAX]	= { };
+
+	int un = montauk::readdir("0:/usr/bin", usr_names, RD_MAX);
+
+	for (int i = 0; i < un; i++) {
+		/* Entries come back as "usr/bin/as.elf"; strip to the last
+		   slash, not the first. */
+		int inc = 0;
+		for (int j = 0; usr_names[i][j]; j++) {
+			if (usr_names[i][j] == '/')
+				inc = j + 1;
+		}
+
+		if (montauk::starts_with(usr_names[i] + inc, (const char*)string)) {
+			if (r >= arrayMax)
+				break;
+
+			if (!is_executable(usr_names[i]))
+				continue;
+
+			char* p = (char *)usr_names[i] + inc;
+			strip_elf_extension(p);
+
+			array[r] = (char *)p;
+			r++;
+		}
+	}
+
 	// ---- Shell builtins ----
 
 	size_t builtins_count = sizeof(shell_builtins) / sizeof(const char*);