Well, 

I thought, I should add a few words in the README
about this feature:

diff --git a/gdb/README b/gdb/README
index e65c5ea..db0a774 100644
--- a/gdb/README
+++ b/gdb/README
@@ -488,6 +488,9 @@ more obscure GDB `configure' options are not listed here.
      Build GDB using the GMP library installed at the directory DIR.
      If your host does not have GMP installed, you can get the latest
      version at `https://gmplib.org/'.
+     You can also build GMP in-tree when you use the script
+     ./contrib/download_prerequisites.  Note however, that this
+     does only work with a separate build directory.
 
 `--with-mpfr'
      Build GDB with GNU MPFR, a library for multiple-precision
@@ -499,6 +502,9 @@ more obscure GDB `configure' options are not listed here.
      available, GDB will fall back to using host floating-point
      arithmetic.  If your host does not have GNU MPFR installed, you
      can get the latest version from `https://www.mpfr.org/'.
+     You can also build MPFR in-tree when you use the script
+     ./contrib/download_prerequisites.  Note however, that this
+     does only work with a separate build directory.
 
 `--with-python[=PYTHON]'
      Build GDB with Python scripting support.  (Done by default if


Tested on x86_64-pc-linux-gnu.
Is it OK for trunk?


Thanks
Bernd.