Make the examples usable as minimal tests

Display the executed commands.
Fix warnings that would be printed on standard error.

examples/Makefile

@@ -2,5 +2,5 @@ PTH := .:$(PATH)
 export PATH=${PTH}
 
 all clean run:
-	-${foreach dir,${wildcard */}, ${MAKE} $@ -C ${dir};}
+	${foreach dir,${wildcard */}, ${MAKE} $@ -C ${dir} && } true
 .PHONY: all clean run

examples/ada_f77/src/fm.adb

@@ -34,7 +34,11 @@
 
 with Ada.Text_IO; use Ada.Text_IO;
 with Ada.Integer_Text_IO;
+pragma Warnings (Off, """System.Parameters"" is An Internal GNAT Unit");
+pragma Warnings (Off, "use of This Unit is Non-Portable and Version-dependent");
 with System.Parameters;
+pragma Warnings (On, """System.Parameters"" is An Internal GNAT Unit");
+pragma Warnings (On, "use of This Unit is Non-Portable and Version-dependent");
 package body FM is
 
    Init_Error : exception;

examples/subsystems/c_src/c_main.c

@@ -1,3 +1,4 @@
+#include <stdlib.h>
 extern void adainit (void);
 extern void adafinal (void);
 extern void do_it_in_ada(void);