Don't hard-code the path of python and don't use non-standard uint type

This merge request fixes build failure on FreeBSD:

[2/525] Compiling C object 'libgda/sqlite/331f0d9@@gen_emb_string@exe/gen_emb_string.c.o'.
FAILED: libgda/sqlite/331f0d9@@gen_emb_string@exe/gen_emb_string.c.o 
clang -B/home/lantw44/.local/bin -Ilibgda/sqlite/331f0d9@@gen_emb_string@exe -Ilibgda/sqlite -I../../source/libgda/libgda/sqlite -Xclang -fcolor-diagnostics -pipe -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -std=gnu11 -O2 -g -march=corei7 -B/home/lantw44/.local/bin -g3 -Og -gz -fdebug-macro -MD -MQ 'libgda/sqlite/331f0d9@@gen_emb_string@exe/gen_emb_string.c.o' -MF 'libgda/sqlite/331f0d9@@gen_emb_string@exe/gen_emb_string.c.o.d' -o 'libgda/sqlite/331f0d9@@gen_emb_string@exe/gen_emb_string.c.o' -c ../../source/libgda/libgda/sqlite/gen_emb_string.c
../../source/libgda/libgda/sqlite/gen_emb_string.c:110:18: error: use of undeclared identifier 'uint'; did you mean 'int'?
                if (n_read != (uint) fsize) {
                               ^~~~
                               int
../../source/libgda/libgda/sqlite/gen_emb_string.c:110:17: error: reference to overloaded function could not be resolved; did you mean to call it?
                if (n_read != (uint) fsize) {
                              ^~~~~~
../../source/libgda/libgda/sqlite/gen_emb_string.c:119:27: error: use of undeclared identifier 'uint'; did you mean 'int'?
                for (i = buffer_index; (uint) i < buffer_index + n_read + added; i++) {
                                        ^~~~
                                        int
../../source/libgda/libgda/sqlite/gen_emb_string.c:119:26: error: reference to overloaded function could not be resolved; did you mean to call it?
                for (i = buffer_index; (uint) i < buffer_index + n_read + added; i++) {
                                       ^~~~~~
../../source/libgda/libgda/sqlite/gen_emb_string.c:120:46: error: use of undeclared identifier 'uint'; did you mean 'int'?
                        if (buffer_index + n_read + added + 2 >= (uint) maxlen) {
                                                                  ^~~~
                                                                  int
../../source/libgda/libgda/sqlite/gen_emb_string.c:120:45: error: reference to overloaded function could not be resolved; did you mean to call it?
                        if (buffer_index + n_read + added + 2 >= (uint) maxlen) {
                                                                 ^~~~~~
6 errors generated.

[195/521] Generating sqlite_specs_add_column.raw.xml with a custom command.
FAILED: providers/sqlite/sqlite_specs_add_column.raw.xml 
/home/lantw44/gnome/source/libgda/providers/raw_spec.py -o /home/lantw44/gnome/build/libgda/providers/sqlite ../../source/libgda/providers/sqlite/sqlite_specs_add_column.xml.in
/bin/sh: /home/lantw44/gnome/source/libgda/providers/raw_spec.py: not found

[88/324] Generating mysql-hander-binc with a custom command.
FAILED: providers/mysql/gda-mysql-handler-bin.c 
/home/lantw44/gnome/source/libgda/providers/mysql/gen_bin.py -o=providers/mysql/gda-mysql-handler-bin.c ../../source/libgda/libgda/sqlite/gda-sqlite-handler-bin.c
/bin/sh: /home/lantw44/gnome/source/libgda/providers/mysql/gen_bin.py: not found
[89/324] Generating mysql-hander-binh with a custom command.
FAILED: providers/mysql/gda-mysql-handler-bin.h 
/home/lantw44/gnome/source/libgda/providers/mysql/gen_bin.py -o=providers/mysql/gda-mysql-handler-bin.h ../../source/libgda/libgda/sqlite/gda-sqlite-handler-bin.h
/bin/sh: /home/lantw44/gnome/source/libgda/providers/mysql/gen_bin.py: not found