[flang] Merge pull request flang-compiler/f18#544 from flang-compiler/jpr-reshape-only-folding

RESHAPE without shared runtime/front-end descriptor API

Original-commit: flang-compiler/f18@24856b82387a6d729b8d50314bc3e67200ec6f86
Reviewed-on: https://github.com/flang-compiler/f18/pull/544

Due to a conflicting rebase during the linearizing of flang-compiler/f18, this commit squashes a number of other commits:

flang-compiler/f18@2ec1d85d398e4171b6d77a21ccbe1fffec9e420d Implement RESHAPE folding on Constant<T> only
flang-compiler/f18@539463053942adf93ae015af800934e73d8942e3 Enable RESHAPE folding tests
flang-compiler/f18@83b2b86253c9536bb5698526d461f4c68c1affaf Answer review comment + Add a common path for intrsinic function folding before specializing the folding per type. + Make reshape folding return an "invalid" intrinsic after errors are met so that warnings do not get re-generated. + Misc style changes
flang-compiler/f18@2e5c29f2805e1e8dfdb8caa8f13eac9472c4c3c2 add missing file to previous commit...
flang-compiler/f18@9bd5ad9875e894a9a86e94f1e2153cc2cd5ef8d5 Document issue #518 workaround
flang-compiler/f18@a4f8f518318f01c298392f3c6e3b8745e34c2953 Go back to clang-format version 7.01
flang-compiler/f18@e871e58a5218504d9c92056058458706f3ad0c27 answer comment regarding naming and interface
flang-compiler/f18@145c7c1ecee57ff557527c0e6eb5655f43f00e39 Merge branch 'master' into jpr-reshape-only-folding Too many logical conflicts to simply rebase.