[Buildroot] [git commit branch/2023.11.x] package/bayer2rgb-neon: fix aarch64 build with BR2_OPTIMIZE_0

[Peter Korsgaard]

commit: https://git.buildroot.net/buildroot/commit/?id=a1af858ee9d8d69cf1272a6a38cc3a0dd658dd4a
branch: https://git.buildroot.net/buildroot/commit/?id=refs/heads/2023.11.x

Fix the following build failure with aarch64 and BR2_OPTIMIZE_0 raised
since commit 0512910e4901edcb78bb1daa4eb3be9bdc4dc8a9:

src/convert-neon-body-bayer8.inc.h: In function 'bayer2rgb_convert_neon':
src/convert-neon.c:233:17: error: third argument to '__builtin_prefetch' must be a constant
  233 |                 __builtin_prefetch(((void const *)(_addr)) + 64, 0, (_lvl)); \
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/convert-neon-body-bayer8.inc.h:8:9: note: in expansion of macro 'do_prefetch'
    8 |         do_prefetch(&in[+1*stride - 1], (rows_per_loop) < 3 ? 3 : 0);
      |         ^~~~~~~~~~~

Fixes:
 - http://autobuild.buildroot.org/results/307c1c448becd99dfba3a17b3ef816db0bb5cad6

Signed-off-by: Fabrice Fontaine <fontaine.fabrice at gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni at bootlin.com>
(cherry picked from commit 13f8df8ed6e69f102d71d2040176b9374ff81706)
Signed-off-by: Peter Korsgaard <peter at korsgaard.com>
---
 package/bayer2rgb-neon/bayer2rgb-neon.mk | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/package/bayer2rgb-neon/bayer2rgb-neon.mk b/package/bayer2rgb-neon/bayer2rgb-neon.mk
index 212fe76766..5147a985e8 100644
--- a/package/bayer2rgb-neon/bayer2rgb-neon.mk
+++ b/package/bayer2rgb-neon/bayer2rgb-neon.mk
@@ -19,6 +19,14 @@ ifeq ($(BR2_arm),y)
 BAYER2RGB_NEON_CFLAGS += -mfpu=neon
 endif
 
+# __builtin_prefetch() third argument must be a constant, but
+# bayer2rgb-neon uses a variable, derived from a constant, so some
+# optimization is needed to allow the compiler to turn it into a
+# constant, otherwise the build fails
+ifeq ($(BR2_OPTIMIZE_0),y)
+BAYER2RGB_NEON_CFLAGS += -O1
+endif
+
 BAYER2RGB_NEON_CONF_ENV = CFLAGS="$(BAYER2RGB_NEON_CFLAGS)"
 
 $(eval $(autotools-package))