Report actual errno / error string from C library calls

[jphickey]

Is your feature request related to a problem? Please describe.
During startup, the PSP makes several calls into C library functions, and an unexpected failure of these functions causes the system to abort/not start. However, the error messages reported do not include any detail of what went wrong.

Example:

PSP/fsw/pc-linux/src/cfe_psp_memory.c

Lines 143 to 147 in 6d40816

	if ((key = ftok(CFE_PSP_CDS_KEY_FILE, 'R')) == -1)
	{
	OS_printf("CFE_PSP: Cannot Create CDS Shared memory key!\n");
	exit(-1);
	}

Describe the solution you'd like
On any system call that sets the global errno value, if that function fails, this should be included in the error that is printed to the console. At a bare minimum, could include the numeric value, but far preferable to use the system library call to print in a more human-friendly form, such as strerror() or perror() if the system provides it.

Additional context
Should probably also not use OS_printf() here due to its extra buffering, see #203, #299

Requester Info
Joseph Hickey, Vantage Systems, Inc.