Fix alignment of vector of floats in babl-rgb-converter.c

This fixes https://bugs.gentoo.org/857708


Signed-off-by: Alexander Bezrukov <phmagic@mail.ru>

diff -ur a/babl/base/babl-rgb-converter.c b/babl/base/babl-rgb-converter.c
--- a/babl/base/babl-rgb-converter.c	2022-07-13 04:20:08.191785228 +0300
+++ b/babl/base/babl-rgb-converter.c	2022-07-13 04:28:38.907988086 +0300
@@ -306,7 +306,8 @@
   uint8_t *rgb_in_u8 = (void*)src_char;
   uint8_t *rgb_out_u8 = (void*)dst_char;
 
-  float rgba_out[4*samples];
+  // The alignment is necessary for SIMD intrinsics in babl_matrix_mul_vectorff_buf4_sse2()
+  float __attribute__ ((aligned (16))) rgba_out[4*samples];
 
   for (i = 0; i < samples; i++)
   {