gcc-4.9.inc: fix parallel building failure

gcc-4.9.inc: fix parallel building failure

In subdir 'gcc', Most C source files included config.h which was
generated by a rule. But no related prerequisites was added to
the C source compiling rule. There was potential building failure
while makefile enabled parallel.

The C source compiling rule used suffix rule '.c.o', but the suffix
rule doesn't support prerequisites.
https://www.gnu.org/software/make/manual/html_node/Suffix-Rules.html

We used the pattern rule '%.o : %.c' to instead, and add the config.h
as its prerequisite

We also moved the '%.o : %.c' rule down to the 'build/%.o :' rule, which
makes '%.o : %.c' rule doesn't override 'build/%.o :'.

[YOCTO #6568]

(From OE-Core rev: 86c2483f0fe05fb763d280ae22d70e54cb4bb0bc)

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>