libubacktrace: Conditionally link libgcc_eh
When libubacktrace is not enabled there is no need to link in libgcc_eh
Fixes bootstrap failures with (gcc-4.5.x) stage1 compilers that --disable-shared
Signed-off-by: Jason Woodward <jason.woodward@timesys.com>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>