Fix -Wmisleading-indentation warning in top.c

Fix -Wmisleading-indentation warning in top.c

When building top.c with this clang (daily build from apt.llvm.org):

    $ clang++-10 --version
    clang version 10.0.0-+20191211091425+f99297176cd-1~exp1~20191211082036.1372

I get:

    /home/smarchi/src/binutils-gdb/gdb/top.c:1549:5: error: misleading indentation; statement is not part of the previous 'if' [-Werror,-Wmisleading-indentation]
        fprintf_filtered (stream, _("\n\
        ^
    /home/smarchi/src/binutils-gdb/gdb/top.c:1543:3: note: previous statement is here
      if (SYSTEM_GDBINIT_DIR[0])
      ^

This looks like a legitimate warning, the fprintf_filtered is too much
indented.  Fix it, and at the same time add a bit of whitespace to make
this function easier to read.

gdb/ChangeLog:

	* top.c (print_gdb_configuration): Adjust indentation.