Fixes XSIMD_INLINE for compilers that don't have always_inline

Small fix for compiler (and linters) that do not have the attribute always_inline.
This avoids a cascade of false positives.

Co-authored-by: JetBrains <contact@jetbrains.com>
Co-authored-by: Marco Barbone <mbarbone@flatironinstitute.org>

Author: DiamonDinoia

include/xsimd/config/xsimd_inline.hpp

@@ -17,6 +17,8 @@
 #elif defined __has_attribute
 #if __has_attribute(always_inline)
 #define XSIMD_INLINE inline __attribute__((always_inline))
+#else
+#define XSIMD_INLINE inline
 #endif
 #elif defined(_MSC_VER)
 #define XSIMD_INLINE inline __forceinline