Ninja: On Windows, select the compiler occurring first in PATH

On Windows, toolchains like MSVC require a set of environment variables
to be configured for the compiler to work correctly.  The scripts that
prepare these environments typically put the compiler's directory ahead
of others in the `PATH`.  Teach the Ninja generators to use this as a
heuristic to select the compiler when none is explicitly specified.

This is not necessary with Makefile generators because each toolchain's
environment comes with its own make tool variant, and the corresponding
Makefile generator (e.g. "NMake Makefiles") automatically implies the
matching compiler.

Fixes: #20585

1 files changed, 2 insertions, 0 deletions

diff --git a/Tests/RunCMake/Ninja/SelectCompiler/1/gcc b/Tests/RunCMake/Ninja/SelectCompiler/1/gcc
new file mode 100755
index 0000000..151dfa6
--- /dev/null
+++ b/Tests/RunCMake/Ninja/SelectCompiler/1/gcc
@@ -0,0 +1,2 @@
+#!/bin/sh
+false