configure: rationalise error messages with meaningful texts

Currently, error messages just state the obvious: a required
component is required. While in some cases, there is not much
else to say, in some other cases we could tell much more.

For example, a missing libstdc++ means no static toolchain.

Also, format error and warning messages in a similar fashion,
with a {error,warning} intro, followed by the message specified
by the caller.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

diff -dur ELFkickers.orig/sstrip/Makefile ELFkickers/sstrip/Makefile

--- ELFkickers.orig/sstrip/Makefile	2001-03-24 12:58:27.000000000 +0100

+++ ELFkickers/sstrip/Makefile	2007-05-31 21:17:18.000000000 +0200

@@ -1,7 +1,7 @@

 #  Makefile for sstrip

 sstrip: sstrip.c

-	gcc -ggdb -Wall -W -o sstrip sstrip.c

+	$(CC) -Wall -W -o sstrip sstrip.c

 clean:

 	rm -f sstrip