configure: Force the C standard to gnu99

Different versions of GCC and Clang use different versions of the C standard.
This repeatedly caused problems already, e.g. with duplicated typedefs:

https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg05829.html

or with for-loop variable initializers:

https://lists.gnu.org/archive/html/qemu-devel/2019-01/msg00237.html

To avoid these problems, we should enforce the C language version to the
same level for all compilers. Since our minimum compiler versions is
GCC v4.8, our best option is "gnu99" for C code right now ("gnu17" is not
available there yet, and "gnu11" is marked as "experimental"), and "gnu++98"
for the few C++ code that we have in the repository.

Backports commit 7be41675f7cb16be7c8d2554add7a63fa43781a8 from qemu
This commit is contained in:
Thomas Huth 2019-01-22 20:18:48 -05:00 committed by Lioncash
parent baf2fe0fc1
commit 72abfa9588
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2
qemu/configure vendored
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@ -241,7 +241,7 @@ ARFLAGS="${ARFLAGS-rv}"
# left shift of signed integers is well defined and has the expected
# 2s-complement style results. (Both clang and gcc agree that it
# provides these semantics.)
QEMU_CFLAGS="-fno-strict-aliasing -fno-common -fwrapv $QEMU_CFLAGS"
QEMU_CFLAGS="-fno-strict-aliasing -fno-common -fwrapv -std=gnu99 $QEMU_CFLAGS"
QEMU_CFLAGS="-Wall -Wundef -Wwrite-strings -Wmissing-prototypes $QEMU_CFLAGS"
QEMU_CFLAGS="-Wstrict-prototypes -Wredundant-decls $QEMU_CFLAGS"
QEMU_CFLAGS="-D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE $QEMU_CFLAGS"