Build: Use AC_LINK_IFELSE instead of -Werror

AC_COMPILE_IFELSE needed -Werror because Clang <= 14 would merely
warn about the unsupported attribute and implicit function declaration.
Changing to AC_LINK_IFELSE handles the implicit declaration because
the symbol __crc32d is unlikely to exist in libc.

Note that the other part of the check is that #include <arm_acle.h>
must work. If the header is missing, most compilers give an error
and the linking step won't be attempted.

Avoiding -Werror makes the check more robust in case CFLAGS contains
warning flags that break -Werror anyway (but this isn't the only check
in configure.ac that has this problem). Using AC_LINK_IFELSE also makes
the check more similar to how it is done in CMakeLists.txt.

(cherry picked from commit 35eb57355ad1c415a838d26192d5af84abb7cf39)

diff --git a/configure.ac b/configure.ac
index 5698cdf5c0660d8a3d27ebc50de984622d485f36..a578e5b828aa4846d99d36eddbf6e76ebe696312 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -1054,15 +1054,7 @@ AC_MSG_CHECKING([if ARM64 CRC32 instruction is usable])
 AS_IF([test "x$enable_arm64_crc32" = xno], [
        AC_MSG_RESULT([no, --disable-arm64-crc32 was used])
 ], [
-       # Set -Werror here because some versions of Clang (14 and older)
-       # do not report the unsupported __attribute__((__target__("+crc")))
-       # or __crc32d() as an error, only as a warning. This does not need
-       # to be done with CMake because tests will attempt to link and the
-       # error will be reported then.
-       OLD_CFLAGS="$CFLAGS"
-       CFLAGS="$CFLAGS -Werror"
-
-       AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
+       AC_LINK_IFELSE([AC_LANG_SOURCE([[
 #include <arm_acle.h>
 #include <stdint.h>
 
@@ -1082,8 +1074,6 @@ int main(void)
                enable_arm64_crc32=no
        ])
        AC_MSG_RESULT([$enable_arm64_crc32])
-
-       CFLAGS="$OLD_CFLAGS"
 ])
 
 # Check for ARM64 CRC32 instruction runtime detection.