cmd/compile: gracefully exit on parser stack overflow

[griesemer]

The go/parser has a mechanism to detect excessive recursion and avoid possible stack overflow (incNestLev, decNestLev). We should implement a similar featured in the compiler's parser (syntax package).

Tracking issue.

[gopherbot]

Change https://go.dev/cl/691755 mentions this issue: syntax: gracefully exit on parser stack overflow