test: permit "exponent too large" error

The language spec only requires a signed binary exponent of 16 bits
for floating point constants. Permit a "exponent too large" error for
larger exponents.

Don't run test 11326b with gccgo, as it requires successful compilation
of floating point constants with exponents that don't fit in 16 bits.

Change-Id: I98688160c76864aba525a151a14aaaf86bc36a6f
Reviewed-on: https://go-review.googlesource.com/c/go/+/279252


Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>