GNUmakefile: add spellfix target, use it. (#4387)

TODO: Remove the go.mod/go.sum in internal/tools once doing so doesn't break CI (e.g. once we drop support for go 1.19)

* builder/cc1as.h: fix typo found by 'make spell'
* GNUmakefile: remove exception for inbetween, fix instance now found by 'make spell'
* GNUmakefile: remove exception for programmmer, fix instance now found by 'make spell'
* go.mod: use updated misspell. GNUmakefile: add spellfix target, use it.
* ignore directories properly when invoking spellchecker.
* make spell: give internal/tools its own go.mod, as misspell requires newer go
* make lint: depend on tools and run the installed revive
(which was perhaps implied by the change that added revive to internal/tools,
but not required in GNUmakefile until we gave internal/tools its own temporary go.mod)
* .github: now that 'make spell' works well, run it from CI
* GNUmakefile: make spell now aborts if it finds misspelt words, so what it finds doesn't get lost in CI logs
* GNUmakefile: tools: avoid -C option on go generate to make test-llvm15-go119 circleci job happy, see
https://cs.opensource.google/go/go/+/2af48cbb7d85e5fdc635e75b99f949010c607786
* internal/tools/go.mod: fix format of go version to leave out patchlevel, else go complains.

src/machine/machine_stm32l0.go

@@ -256,10 +256,10 @@ func (spi SPI) getBaudRate(config SPIConfig) uint32 {
 	}
 
 	// set frequency dependent on PCLK prescaler. Since these are rather weird
-	// speeds due to the CPU freqency, pick a range up to that frquency for
+	// speeds due to the CPU frequency, pick a range up to that frequency for
 	// clients to use more human-understandable numbers, e.g. nearest 100KHz
 
-	// These are based on APB2 clock frquency (84MHz on the discovery board)
+	// These are based on APB2 clock frequency (84MHz on the discovery board)
 	// TODO: also include the MCU/APB clock setting in the equation
 	switch {
 	case localFrequency < 328125: