Avoid implicit float <-> integer conversion warnings

On:

 $ uname -a
 NetBSD gcc70.fsffrance.org 5.1 NetBSD 5.1 (GENERIC) #0: Sat Nov  6 13:19:33 UTC 2010  builds@b6.netbsd.org:/home/builds/ab/netbsd-5-1-RELEASE/amd64/201011061943Z-obj/home/builds/ab/netbsd-5-1-RELEASE/src/sys/arch/amd64/compile/GENERIC amd64

With:

 $ g++ -v
 Using built-in specs.
 Target: x86_64--netbsd
 Configured with: /usr/src/tools/gcc/../../gnu/dist/gcc4/configure --enable-long-long --disable-multilib --enable-threads --disable-symvers --build=x86_64-unknown-netbsd4.99.72 --host=x86_64--netbsd --target=x86_64--netbsd --enable-__cxa_atexit
 Thread model: posix
 gcc version 4.1.3 20080704 prerelease (NetBSD nb2 20081120)

I saw:

 ../../src/gdb/ada-typeprint.c: In function 'void print_fixed_point_type(type*, ui_file*)':
 ../../src/gdb/ada-typeprint.c:366: warning: passing 'float' for argument 2 to 'DOUBLEST ada_fixed_to_float(type*, LONGEST)'

 ../../src/gdb/value.c: In function 'LONGEST unpack_long(type*, const gdb_byte*)':
 ../../src/gdb/value.c:2833: warning: converting to 'LONGEST' from 'DOUBLEST'
 ../../src/gdb/value.c:2838: warning: converting to 'LONGEST' from 'DOUBLEST'

gdb/ChangeLog:
2016-04-14  Pedro Alves  <palves@redhat.com>

	* ada-typeprint.c (print_fixed_point_type): Don't pass float as
	argument to function expecting LONGEST.
	* value.c (unpack_long): Add casts to LONGEST.