[DTLTO][TEST] Fix Clang driver test failing on some build bots

Not all builds name the compiler executable `clang`. For example,
the Fuchsia build bots use `llvm` as the executable name, as they
combine everything together in a busybot-style binary.

Update the Clang driver test to simply check that a non-empty path
is provided for the `--thinlto-remote-compiler` argument, rather
than hardcoding the executable name. The cross-project test will
verify that the path is valid later.

Should fix #147265.

Author: bd1976bris

clang/test/Driver/DTLTO/dtlto.c

@@ -10,7 +10,7 @@
 
 // FORWARD: ld.lld
 // FORWARD-SAME: "--thinlto-distributor=d.exe"
-// FORWARD-SAME: "--thinlto-remote-compiler={{.*}}clang{{[^\"]*}}"
+// FORWARD-SAME: "--thinlto-remote-compiler={{[^"]+}}"
 // FORWARD-SAME: "--thinlto-distributor-arg=a1"
 // FORWARD-SAME: "--thinlto-distributor-arg=a2"
 // FORWARD-SAME: "--thinlto-distributor-arg=a3"