RFR: JDK-8077113: Configure script do not properly detect cross-compilation gcc

[Tim Bell]

Erik:

> When doing cross-compilation, a tool like nm gets picked up like
> '<platform>-linux-gnu-nm' but '<platform>-linux-gnu-gcc' will not. My
> fix uses AC_PATH_TOOL instead of AC_PATH_PROGS when actually searching
> for the compilers, which will look for the prefixed version of the tool
> first. The only drawback is that AC_PATH_TOOL does not accept multiple
> program names to search for, but we don't use that anyway. For each
> toolchain type, we only ever expect one name for the compiler. If we
> need to support multiple names, we can add a loop then.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8077113
>
> Webrev: http://cr.openjdk.java.net/~erikj/8077133/webrev.01/

Looks good

Tim