Move the closure of the subset of flang/runtime/*.h header files that
are referenced by source files outside flang/runtime (apart from unit tests)
into a new directory (flang/include/flang/Runtime) so that relative
include paths into ../runtime need not be used.

flang/runtime/pgmath.h.inc is moved to flang/include/flang/Evaluate;
it's not used by the runtime.

Differential Revision: https://reviews.llvm.org/D109107

result descriptor (e.g., maxloc, minloc, maxval, minval, all, any, count,
parity, findloc, etc.)

Also add a scalar case for these intrinsic unit tests.

Differential Revision: https://reviews.llvm.org/D106820

We had IPARITY (xor-reduction) but I missed IALL (and)
and IANY (or).

Differential Revision: https://reviews.llvm.org/D104339

Implement constant folding for the reduction transformational
intrinsic functions MAXVAL and MINVAL.

In anticipation of more folding work to follow, with (I hope)
some common infrastructure, these two have been implemented in a
new header file.

Differential Revision: https://reviews.llvm.org/D104337

API, implementation, and basic tests for the transformational
reduction intrinsic function DOT_PRODUCT in the runtime support
library.

Differential Revision: https://reviews.llvm.org/D102351

Implement the reduction transformational intrinsic function NORM2 in
the runtime, using infrastructure already in place for MAXVAL & al.

Differential Revision: https://reviews.llvm.org/D102024

The single source file reduction.cpp is a little large in
terms of both source lines and generated text bytes, so
split SUM, PRODUCT, FINDLOC, and MAXLOC/MAXVAL/MINLOC/MINVAL
off into their own C++ source files that share a set of
implementation function templates now in a common header.

Differential Revision: https://reviews.llvm.org/D101111

Define APIs for, and implement, these three more recently-introduced
standard reduction transformational intrinsic functions to the runtime.

Differential Revision: https://reviews.llvm.org/D100863

Move #include <complex.h> to complex-reduction.h, where
it is needed in MSVC builds.

Exclude code that requires a native 128-bit integer type from
compilation by MSVC.

Differential Revision: https://reviews.llvm.org/D99806

Add runtime APIs, implementations, and tests for ALL, ANY, COUNT,
MAXLOC, MAXVAL, MINLOC, MINVAL, PRODUCT, and SUM reduction
transformantional intrinsic functions for all relevant argument
and result types and kinds, both without DIM= arguments
(total reductions) and with (partial reductions).

Complex-valued reductions have their APIs in C so that
C's _Complex types can be used for their results.

Some infrastructure work was also necessary or noticed:
* Usage of "long double" in the compiler was cleaned up a
  bit, and host dependences on x86 / MSVC have been isolated
  in a new Common/long-double header.
* Character comparison has been exposed via an extern template
  so that reductions could use it.
* Mappings from Fortran type category/kind to host C++ types
  and vice versa have been isolated into runtime/cpp-type.h and
  then used throughout the runtime as appropriate.
* The portable 128-bit integer package in Common/uint128.h
  was generalized to support signed comparisons.
* Bugs in descriptor indexing code were fixed.

Differential Revision: https://reviews.llvm.org/D99666