This fixes an issue introduced in Ada 2012 for calls to functions taking
an In/Out parameter and for which the actual is the component of a
packed array.  In this case, the front-end needs to create a temporary
for the actual, initialize it before the call and assign it back after
it, because operations on bit-packed arrays are converted into
mask-and-shift sequences.

Tested on x86_64-pc-linux-gnu, committed on trunk

2019-07-05  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* exp_ch4.adb (Expand_N_Indexed_Component): Do not expand actual
	parameters of function calls here either.

gcc/testsuite/

	* gnat.dg/pack23.adb, gnat.dg/pack23_pkg.ads: New testcase.