F01, the driver is an interpreter

[tamnd]

The first lesson of M3. T01 showed which programs gcc runs; this shows the language that decision is written in, and ends by changing it.

What is new

gxray/specs.py, a reader for gcc -dumpspecs. Forty five % forms in five families, the three compound forms (%{, %:, %(), where an argument ends, brace predicates in words, and the call graph. It is a reader and not a second interpreter: it substitutes nothing, because substituting would need a command line, a target, a filesystem and a temporary directory.

corpora/specs/f01.json, two whole spec tables of the same release (aarch64 Darwin, 56 blocks; x86-64 Linux through Compiler Explorer, 47 blocks), plus what the driver has compiled into it (static_specs, the spec functions, the compiler table's suffixes and language rows), plus four pairs of -### runs that differ by one text file:

file	before	after
argument	cc1	cc1, with -fverbose-asm
assembler	cc1, as	cc1, my-own-assembler
guard	cc1	cc1, as
suffix	nothing, and a warning	cc1, as

The guard file is the invoke_as spec with its %{!S: wrapper removed, so gcc -S runs the assembler. guard and assembler are derived from the live local invoke_as rather than written down, so re-recording on another target is still a fair test rather than an embedded Darwin string.

tests/test_specs.py, 51 tests. The one that matters compares FORMS against the case '...' labels of do_spec_1 when vendor/gcc is checked out: a GCC that grows a % form now fails the build rather than having a lesson print it as text.

blueprints/BP-DRIVER.md goes from stub to partial. The spec language in full with a table per family, the specs file format and its two kinds of entry, EXTRA_SPEC_FUNCTIONS as the reason 21 spec functions is a floor, two new invariants (every %(name) resolves; a name defined twice resolves to the last), and what the two recorded targets say about the cost of a port.

Four glossary terms: spec rewritten, and spec function, compiler table, specs file added.

Gates

pytest -q 1504 passed, ruff check, ruff format --check, refcheck check 507 citations, nbbuild build|check|claims|verify|index, nbbuild run 18 lessons in a real kernel, prosecheck 46 files, bpc check|pages --check, tier0 check|coverage|offline|online 31 experiments, dumpparse check, matrix table --check, gxray.glossary 92 terms.

matrix digests --check still reports the two missing boot digests, which is the open M2 gate and not from this branch.