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

[Erik Joelsson]

Hello,

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/

/Erik