[flang][runtime] Formatted input optimizations (#134715)
Make some minor tweaks (inlining, caching) to the formatting input path
to improve integer input in a SPEC code. (None of the I/O library has
been tuned yet for performance, and there are some easy optimizations
for common cases.) Input integer values are now calculated with native
C/C++ 128-bit integers.
A benchmark that only reads about 5M lines of three integer values each
speeds up from over 8 seconds to under 3 in my environment with these
changeds.
If this works out, the code here can be used to optimize the formatted
input paths for real and character data, too.
Fixes https://github.com/llvm/llvm-project/issues/134026.
