a.out left in root directory when configuring --with-toolchain-type=clang

[Martin Buchholz]

I notice that running bash ./configure ... leaves an a.out file in the root
directory of the jdk, but only after adding configure flags

--with-toolchain-type=clang --with-toolchain-path=/usr/lib/llvm-3.9/bin

(i.e. not when building with default gcc)

Probably there's a test compilation whose output does not go into the
build/ directory, and whose output is not cleaned up.