Parse errors during Rcpp::compileAttributes() cause Build pane to 'freeze'

[kevinushey]

To reproduce, try working on an R package that contains compiled C / C++ code. In my case, I reproduced this using the reticulate package. To reproduce, try doing the following:

writeLines("x <-", "R/ouch.R")

then invoking a Install and Restart (Build and Reload) with Ctrl + Shift + B. You should see something like:

and attempts to press the Stop button, or start new builds, will fail.

[kevinushey]

Relevant code likely lives here: https://github.com/rstudio/rstudio/blob/master/src/cpp/session/modules/build/SessionBuild.cpp#L514-L550

[jmcphers]

Backported to 1.1 here: 881134b

[dfalty]

Verified fixed 1.1.392.