[src] Fix compilation of `crc32.c` on aarch64 with Clang (#44915)
Compilation of this file on aarch64 Linux with Clang currently fails with
```console
$ make crc32c.o CC=clang
CC src/crc32c.o
In file included from /home/mose/repo/julia/src/crc32c.c:45:
In file included from ./julia_internal.h:1021:
In file included from /home/mose/repo/julia/usr/include/libunwind.h:7:
/home/mose/repo/julia/usr/include/libunwind-aarch64.h:60:9: warning: empty struct has size 0 in C, size 1 in C++ [-Wc++-compat]
typedef struct
^
/home/mose/repo/julia/usr/include/libunwind-aarch64.h:169:9: warning: empty struct has size 0 in C, size 1 in C++ [-Wc++-compat]
typedef struct unw_tdep_save_loc
^
/home/mose/repo/julia/src/crc32c.c:339:22: warning: unused function 'crc32c_dispatch' [-Wunused-function]
static crc32c_func_t crc32c_dispatch(unsigned long hwcap)
^
'++crc' is not a recognized feature for this target (ignoring feature)
'++crc' is not a recognized feature for this target (ignoring feature)
/home/mose/repo/julia/src/crc32c.c:212:9: error: instruction requires: crc
asm("crc32cx %w0, %w1, %2" : "=r"(res) : "r"(crc), "r"(val));
^
<inline asm>:1:2: note: instantiated into assembly here
crc32cx w0, w0, x1
^
/home/mose/repo/julia/src/crc32c.c:218:9: error: instruction requires: crc
asm("crc32cw %w0, %w1, %w2" : "=r"(res) : "r"(crc), "r"(val));
^
<inline asm>:1:2: note: instantiated into assembly here
crc32cw w0, w0, w1
^
/home/mose/repo/julia/src/crc32c.c:224:9: error: instruction requires: crc
asm("crc32ch %w0, %w1, %w2" : "=r"(res) : "r"(crc), "r"(val));
^
<inline asm>:1:2: note: instantiated into assembly here
crc32ch w0, w0, w1
^
/home/mose/repo/julia/src/crc32c.c:230:9: error: instruction requires: crc
asm("crc32cb %w0, %w1, %w2" : "=r"(res) : "r"(crc), "r"(val));
^
<inline asm>:1:2: note: instantiated into assembly here
crc32cb w0, w0, w1
^
3 warnings and 4 errors generated.
make: *** [Makefile:217: crc32c.o] Error 1
```
Compilation on aarch64 macOS with Apple Clang is successful, but there is still
the message about the unrecognized feature:
```console
% rm -f crc32c.o; make crc32c.o
CC src/crc32c.o
'++crc' is not a recognized feature for this target (ignoring feature)
'++crc' is not a recognized feature for this target (ignoring feature)
```
It appears GCC and Clang disagrees on how the target attribute should be
specified: GCC wants `"+crc"`, while Clang wants `"crc"`. Also Android's zlib
uses `"crc"` only when building for Clang: <https://android.googlesource.com/platform/external/zlib/+/refs/tags/android-platform-12.1.0_r2/crc32_simd.c#187>.
With this change, compilation of Julia on aarch64 Linux with Clang is now
successful.
Co-authored-by: Dilum Aluthge <dilum@aluthge.com>
