If you have multiple llvm-config executables in your path, and all of
them cause failures, then only the last failure will be printed. This
can cause confusion when the multiple llvm-config executables are from
different major LLVM versions, i.e. LLVM 13 and 14, which might mask an
error that happened on the LLVM 14 llvm-config with an unrelated error.
This commit makes it so that all errors are collected into a list and
printed all at once; this way, you can see how each llvm-config
executable failed to configure properly. Note that the failures still
won't be printed if a successful configuration is found.
b35490c217