Commit
30b3db5cca27d98d903b7313073ea272ada36d56
by Oliver SmithRevert `configure: regular_C(PP)FLAGS -> C(PP)FLAGS`
This commit reverts dd335ef8fc41567e324a3d26f1ec30d04c69a0bb.
Observed:
```
$ configure && make CPPFLAGS=-DNDEBUG
gcc -DHAVE_CONFIG_H -I. -I.. -DNDEBUG -I../include -I/usr/include/libmnl -DNDEBUG -Wall -Waggregate-return -Wmissing-declarations -Wmissing-prototypes -Wshadow -Wstrict-prototypes -Wformat=2 -pipe -std=gnu11 -fvisibility=hidden -Wall -Waggregate-return -Wmissing-declarations -Wmissing-prototypes -Wshadow -Wstrict-prototypes -Wformat=2 -pipe -std=gnu11 -MT gtp-tunnel.o -MD -MP -MF $depbase.Tpo -c -o gtp-tunnel.o gtp-tunnel.c &&\
```
Expected:
```
gcc -DHAVE_CONFIG_H -I. -I.. -D_FILE_OFFSET_BITS=64 -D_REENTRANT -I../include -I/usr/include/libmnl -D_FILE_OFFSET_BITS=64 -D_REENTRANT -Wall -Waggregate-return -Wmissing-declarations -Wmissing-prototypes -Wshadow -Wstrict-prototypes -Wformat=2 -pipe -std=gnu11 -fvisibility=hidden -Wall -Waggregate-return -Wmissing-declarations -Wmissing-prototypes -Wshadow -Wstrict-prototypes -Wformat=2 -pipe -std=gnu11 -MT gtp-tunnel.o -MD -MP -MF $depbase.Tpo -c -o gtp-tunnel.o gtp-tunnel.c &&\
```
Including ${CFLAGS} in AM_CFLAGS (which is totally wrong)
is the cause for the double apperance of -DNDEBUG.
_FILE_OFFSET_BITS is lost because dd335 violated one core principle
of autoconf/automake: configure MUST run idempotent and not touch
CPPFLAGS and CFLAGS, pursuant to automake.info ยง3.6 "User variables".
Change-Id: I5cc30885cec564346997269b51decbbe49548ddf