Add telltale error handling in void functions

[baentsch]

Many OQS functions return void "for historical reasons". Nevertheless they can fail. Right now two (pretty user unfriendly) macros are used (sporadically) to react to internal failures:

liboqs/src/common/common.h

Lines 22 to 49 in 9f912c9

	/**
	* Macro for terminating the program if x is
	* a null pointer.
	*/
	#define OQS_EXIT_IF_NULLPTR(x) \
	do { \
	if ( (x) == (void*)0 ) \
	exit(EXIT_FAILURE); \
	} while (0)
	/**
	* This macro is intended to replace those assert()s
	* involving side-effecting statements in aes/aes_ossl.c.
	*
	* assert() becomes a no-op when -DNDEBUG is defined,
	* which causes compilation failures when the statement
	* being checked also results in side-effects.
	*
	* This is a temporary workaround until a better error
	* handling strategy is developed.
	*/
	#define OQS_OPENSSL_GUARD(x) \
	do { \
	if( 1 != (x) ) { \
	exit(EXIT_FAILURE); \
	} \
	} while (0)

This issue is to recommend improving them, e.g., along the lines suggested in #1454 (comment) and then use them in all cases.