gdb: Update embedded Python to Python 3

Use Python 3.7 from /usr/local/system/python3.

We can no longer use gdbs --with-pythons, because it is totaly broken.
Instead of python-config.py from the package specified with
--with-python, a copy of an old python-config.py script from Python-2.7 is
embedded and used with the interpreter found via --with-python.

In our case, the required "-L" option is not returned.

However, if we add the needed CPPFLAGS and LDFLAGS, gdb/configure (run
during the build phase of the top level directory!) will notice that
Python just works.

gdb.be0

@@ -20,9 +20,10 @@ SRCURL[0]="http://ftp.gnu.org/gnu/gdb/gdb-${PKGVERSION}.tar.xz"
 #}
 
 mee_configure() {
-    bee_configure --with-python=/usr/local/system/python2 \
-		CFLAGS="-L/usr/local/system/python2/lib -Wl,-rpath=/usr/local/system/python2/lib" \
-		CXXFLAGS="-L/usr/local/system/python2/lib -Wl,-rpath=/usr/local/system/python2/lib"
+
+    bee_configure \
+        CPPFLAGS="-I/usr/local/system/python3/include/python3.7m" \
+        LDFLAGS="-L/usr/local/system/python3/lib -Wl,-rpath=/usr/local/system/python3/lib -lpython3.7m"
 }
 
 #mee_build() {