The compiler is written in Finch, and nothing else: src/*.fch, built from a seed

boot/ is src/ now. The C++ compiler and CMake are gone from this branch (they are on before-bootstrap).
bootstrap/build.sh builds the compiler from bootstrap/<system>.ll -- the compiler's own LLVM IR -- then builds
it with itself and checks the two come out identical. bootstrap/build.sh seed writes the seed anew.

The driver is complete: the runtime is compiled once and kept in ~/.cache/finch; a program's own C files,
.o and .a files and frameworks link along; a linker failure is read and answered with  link "lib"  or the
library that is missing. The old tests/fail diagnostics are all in again (a missing import, a str compared with
null, 'write just the library's name', a map key that is a float, non-ASCII names, ...).

tests/run.sh is the one test runner: programs, refusals, -g builds and the shared library. 106 passed.

bootstrap/build.sh

@@ -0,0 +1,49 @@
+#!/bin/sh
+# Builds the Finch compiler without a compiler for Finch: from the seed (the compiler's own LLVM IR),
+# then from itself, and checks that the two come out the same.
+#
+#   bootstrap/build.sh            build/finch
+#   bootstrap/build.sh seed       also write bootstrap/<system>.ll anew (do this when the compiler got a feature
+#                                 its own source uses, or the seed is old: the next build starts from it)
+#
+# Needs clang and libclang (the C headers are read through it). The compiler is then in build/finch; it looks for the
+# runtime and the standard library next to build/, in runtime/ and std/.
+set -eu
+cd "$(dirname "$0")/.."
+mkdir -p build
+
+case "$(uname -s)-$(uname -m)" in
+    Linux-x86_64)                 seed=linux-x86_64 ;;
+    Linux-aarch64|Linux-arm64)    seed=linux-aarch64 ;;
+    Darwin-arm64)                 seed=macos-arm64 ;;
+    Darwin-x86_64)                seed=macos-x86_64 ;;
+    MINGW*|MSYS*|CYGWIN*)         seed=windows-x86_64 ;;
+    *) echo "bootstrap: no seed for $(uname -s) $(uname -m) (see bootstrap/README.md)" >&2; exit 1 ;;
+esac
+[ -f "bootstrap/$seed.ll" ] || { echo "bootstrap: bootstrap/$seed.ll is missing" >&2; exit 1; }
+
+CLANG=${FINCH_CLANG:-clang}
+LIBS=${FINCH_LIBCLANG:--lclang}
+export FINCH_RT=$PWD/runtime/finch_rt.c
+
+echo "bootstrap: seed ($seed) -> build/finch0"
+$CLANG -O1 -w "bootstrap/$seed.ll" runtime/finch_rt.c -o build/finch0 -lm $LIBS
+echo "bootstrap: build/finch0 builds the compiler -> build/finch1"
+build/finch0 build src/main.fch -o build/finch1
+echo "bootstrap: build/finch1 builds the compiler -> build/finch"
+build/finch1 build src/main.fch -o build/finch
+
+# a compiler that builds itself must come out the same however many times it does
+build/finch1 ir src/main.fch > build/stage1.ll
+build/finch ir src/main.fch > build/stage2.ll
+if cmp -s build/stage1.ll build/stage2.ll; then
+    echo "bootstrap: build/finch1 and build/finch make the same IR ($(wc -l < build/stage2.ll) lines): done"
+else
+    echo "bootstrap: the compiler does not reproduce itself (build/stage1.ll and build/stage2.ll differ)" >&2
+    exit 1
+fi
+
+if [ "${1:-}" = seed ]; then
+    cp build/stage2.ll "bootstrap/$seed.ll"
+    echo "bootstrap: wrote bootstrap/$seed.ll"
+fi