Replace includes of build.h with version.h

As build.h is an auto-generated file it was necessary to add it as
an explicit prerequisite in the Makefiles. When this was forgotten
abuild would sometimes fail with following error:

   fatal error: build.h: No such file or directory

Fix this error by compiling version.c into all stages.

Change-Id: I342f341077cc7496aed279b00baaa957aa2af0db
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/7510
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>

src/include/string.h

@@ -56,6 +56,16 @@ static inline char *strdup(const char *s)
 	memcpy(d, s, sz);
 	return d;
 }
+
+static inline char *strconcat(const char *s1, const char *s2)
+{
+	size_t sz_1 = strlen(s1);
+	size_t sz_2 = strlen(s2);
+	char *d = malloc(sz_1 + sz_2 + 1);
+	memcpy(d, s1, sz_1);
+	memcpy(d + sz_1, s2, sz_2 + 1);
+	return d;
+}
 #endif
 
 static inline char *strncpy(char *to, const char *from, int count)