v1.0.0

The toolchain stands on its own. v0.1.0 said the number would reach 1.0.0
"when the toolchain stands on its own, not when the language does" — and this is
that release. selfhost/compiler.pas is the only compiler, seed/pascalc.ll
builds it, and a clone with no C++ compiler and no LLVM development files
compiles the compiler, passes 435 tests, reaches the stage-2/stage-3 fixed point
and proves 43 SMT rules.

The language is unchanged from 0.1.0 — both standards were already complete. The
major version is about what it takes to build this, and about pascalc-s0
disappearing from the command line.

Removed

• Stage 0, the C++ compiler. src/ and selfhost/difftest.sh are deleted;
  selfhost/compiler.pas is the only compiler. seed/pascalc.ll — a working
  compiler in LLVM IR, committed — is what builds it, so a checkout still builds
  itself. (ADR-0085)
• LLVM as a build dependency. Nothing links libLLVM; cmake needs no
  LLVM_DIR, only clang on PATH to assemble IR.
• The differential test, which compared two independent implementations over 436
  sources. Nothing replaces it, and ADR-0085 says what that costs.

Added

• tools/pascalcc — compile and link. pascalc writes IR and stops,
  permanently: no standard Pascal program can start an assembler.
• --dump-tokens, --dump-ast, --dump-sema, --dump-all on pascalc, and
  157 error-path sources adopted as real test cases with .err goldens, taking
  the suite from 279 to 435.

Changed

• pascalc is quiet on success and writes file:line:col: error: message
  on failure, where it used to write three dump sections unconditionally.
• The repository is x86-64 Linux only: the seed carries a target triple.
  Tag v0.1.0 is the last commit where a C++ compiler could reproduce a
  compiler from source alone.

Fixed

• cmake --build left a stale build/bin/pascalc when the compiler failed to
  build, so ctest passed against a compiler that did not match the source.
• A fresh configure could not create build/bin once no C++ executable target
  remained.
• selfhost/badparse/variant-in-variant.pas had been accepted by both compilers
  since ADR-0026 and was no longer a negative test; a differential oracle cannot
  see a test that has stopped testing anything. Deleted — the feature is covered
  by tests/nested_variants.pas.