Prepare for the move to Fedora

tools/posix/setup-fedora.sh installs the toolchain and reports what it
cannot: PowerShell has no Fedora package, and bootcheck is the test
suite, so the script says how to get pwsh rather than failing quietly.
It also checks /dev/kvm, since a Ryzen box can run the tests at native
speed.

docs/moving-to-linux.md is the actual procedure: copy the repo, restore
the memory, install, build. The memory travels inside the repo and
`memory-sync.sh import` puts it under the key this machine derives from
its own path -- /home/nexoniarz/Documents/SchOS becomes
-home-nexoniarz-Documents-SchOS, where D:\DEV\SchOS was D--DEV-SchOS.

OVMF discovery no longer assumes QEMU's Windows layout. Fedora ships
edk2-ovmf to /usr/share/edk2/ovmf/, Debian and Arch differ again, so the
Makefile searches a list and names the packages when it finds nothing.
Tested through the shell rather than $(wildcard): on Windows make is a
native binary using Win32 file calls, while `command -v` returns an MSYS
path like /c/Users/..., which $(wildcard) cannot see -- it returned
nothing on a machine that had the firmware.

Two things only that machine can test: `make ports` builds musl, toybox
and mksh from source, which Windows cannot do at all; and the SchFS
round-trip needs symlinks and hard links, so it has never actually run.

tools/posix/setup-fedora.sh

@@ -0,0 +1,94 @@
+#!/bin/sh
+# Install what SchOS needs to build and test, on Fedora.
+#
+#   tools/posix/setup-fedora.sh          install everything
+#   tools/posix/setup-fedora.sh --check  report what is missing, install nothing
+#
+# Written for Fedora 44. Package names are stable enough that older and newer
+# releases should work unchanged; the --check mode exists so a wrong guess
+# reports itself instead of failing halfway through a dnf transaction.
+
+set -eu
+
+CHECK=0
+[ "${1:-}" = "--check" ] && CHECK=1
+
+# Toolchain. clang and lld are the whole cross-compiler story -- see
+# docs/building.md for why there is no cross-gcc here.
+PKGS="clang lld llvm make gcc perl-interpreter python3 git"
+
+# Running and testing.
+PKGS="$PKGS qemu-system-x86 edk2-ovmf xorriso"
+
+# mtools is for building a real FAT ESP image. Not needed yet -- the UEFI
+# target serves a directory as FAT through QEMU -- but it is what `make iso`
+# will want once the ISO carries an EFI entry.
+PKGS="$PKGS mtools"
+
+# Ports are built from source on this host, which is the reason a Linux box
+# matters: they cannot be built on Windows at all.
+PKGS="$PKGS tar curl xz bzip2 diffutils findutils"
+
+missing=""
+for p in $PKGS; do
+    rpm -q "$p" >/dev/null 2>&1 || missing="$missing $p"
+done
+
+if [ -z "$missing" ]; then
+    echo "all packages present"
+else
+    echo "missing:$missing"
+    if [ "$CHECK" -eq 0 ]; then
+        echo
+        echo "installing..."
+        sudo dnf install -y $missing
+    fi
+fi
+
+# PowerShell is not in Fedora's repositories and is not an rpm you can name.
+#
+# It matters because tools/windows/bootcheck.ps1 is the test harness, and pwsh
+# runs it on Linux perfectly well -- there is simply no dnf package. Microsoft
+# publish a repo; the tarball is the lighter option and needs no root beyond
+# the install path.
+if command -v pwsh >/dev/null 2>&1; then
+    echo "pwsh: $(command -v pwsh)"
+else
+    cat <<'EOF'
+
+pwsh is not installed. tools/windows/bootcheck.ps1 is the boot test suite and
+needs it. Either:
+
+  sudo dnf install -y https://packages.microsoft.com/config/rhel/9/packages-microsoft-prod.rpm
+  sudo dnf install -y powershell
+
+or take the tarball from https://github.com/PowerShell/PowerShell/releases and
+put pwsh on PATH. Nothing else in the build depends on it -- `make`,
+`make schfs-check` and `make qemu` all work without.
+EOF
+fi
+
+echo
+echo "checks:"
+for t in clang ld.lld llvm-objcopy make gcc perl python3 qemu-system-x86_64 xorriso; do
+    if command -v "$t" >/dev/null 2>&1; then
+        printf '  %-22s ok\n' "$t"
+    else
+        printf '  %-22s MISSING\n' "$t"
+    fi
+done
+
+# KVM is the difference between a boot test that takes seconds and one that
+# takes half a minute. It needs the module loaded and the user in the kvm
+# group; a Ryzen box has it unless virtualisation is off in firmware.
+echo
+if [ -e /dev/kvm ]; then
+    if [ -r /dev/kvm ] && [ -w /dev/kvm ]; then
+        echo "kvm: available and usable -- add -enable-kvm to QEMU for much faster boots"
+    else
+        echo "kvm: present but not accessible. Fix with:"
+        echo "  sudo usermod -aG kvm $(id -un) && newgrp kvm"
+    fi
+else
+    echo "kvm: /dev/kvm missing -- check that SVM/virtualisation is enabled in firmware"
+fi