swift234

If there was an error in the build config, continue to parse

r32195 introduced new behavior when there was an error with a build
config: if there was an error, never parse. This was to prevent noise
when a block of code guarded by a _compiler_version clause was
syntatically wrong/misspelled, making it active when it shouldn't have
been. This supressed parsing blocks guarded by other build configs,
which is kind of a regression since, until _compiler_version, all build
configs were always parsed, even if their clauses are inactive. Skipping
parsing may hinder indentation, code folding, and parse-aware
highlighting.

If there is a valid switch on _compiler_version, continue to
skip parsing and supress Lex diagnostics for inactive blocks. If there
is an error evaluating a build config, parse all of its blocks.

rdar://problem/22730282

Swift SVN r32205