Fix Configure.pl --asan flag on clang

Let clang link in its own version of asan instead of supplying -lasan to
the linker. Otherwise there is a version conflict.

Author: samcv

Configure.pl

@@ -327,7 +327,7 @@ ($$)
 $config{ldlibs} = join ' ',
     (map { sprintf $config{ldusr}, $_; } @{$config{usrlibs}}),
     (map { sprintf $config{ldsys}, $_; } @{$config{syslibs}});
-$config{ldlibs} = ' -lasan ' . $config{ldlibs} if $args{asan} and $^O ne 'darwin';
+$config{ldlibs} = ' -lasan ' . $config{ldlibs} if $args{asan} && $^O ne 'darwin' && $config{cc} ne 'clang';
 $config{ldlibs} = ' -lubsan ' . $config{ldlibs} if $args{ubsan} and $^O ne 'darwin';
 # macro defs
 $config{ccdefflags} = join ' ', map { $config{ccdef} . $_ } @{$config{defs}};