cmd, core, ethdb: enable Pebble on 32 bits and OpenBSD too

[karalabe]

Supposedly upstream supports both now.

[holiman]

ethdb\pebble\pebble.go:150:21: cannot use 4 << 30 - 1 (untyped int constant 4294967295) as int value in assignment (overflows)

[holiman]

It's a constant we took from pebble, and have updated it upstream now: https://github.com/cockroachdb/pebble/blob/master/open.go#L57C44-L57C44

	// The max memtable size is limited by the uint32 offsets stored in
	// internal/arenaskl.node, DeferredBatchOp, and flushableBatchEntry.
	//
	// We limit the size to MaxUint32 (just short of 4GB) so that the exclusive
	// end of an allocation fits in uint32.
	//
	// On 32-bit systems, slices are naturally limited to MaxInt (just short of
	// 2GB).
	maxMemTableSize = constants.MaxUint32OrInt

const (
	// oneIf64Bit is 1 on 64-bit platforms and 0 on 32-bit platforms.
	oneIf64Bit = ^uint(0) >> 63

	// MaxUint32OrInt returns min(MaxUint32, MaxInt), i.e
	// - MaxUint32 on 64-bit platforms;
	// - MaxInt on 32-bit platforms.
	// It is used when slices are limited to Uint32 on 64-bit platforms (the
	// length limit for slices is naturally MaxInt on 32-bit platforms).
	MaxUint32OrInt = (1<<31)<<oneIf64Bit - 1
)

[gballet]

Tried with --dev and --synctarget on 64bit OpenBSD, geth compiles, starts and starts syncing

[karalabe]

@holiman Thanks. Updated the constant to be in line with Pebble. PTAL

[karalabe]

@gballet TY!

[holiman]

LGTM