Compiler/IAR: search for both IAR's binaries * and *.exe

IAR is available for both Linux and Windows OSes.  Moreover,
binaries `*.exe` could be called from a Linux box, or vice versa.
See also commit 01a4eec4 (IAR: Changes required for Linux,
2019-04-25, v3.15.0-rc1~185^2).

Fixes: #22312