[clang] [llvm] [clang][RISCV] Use macro to check if intrinsics are supported (PR #187197)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `intel-sycl-gpu` running on `intel-sycl-gpu-01` while building `clang` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/225/builds/7464

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'Clang :: Preprocessor/riscv-intrinsic-exts.c' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 5
/home/test-user/llvm-buildbot-worker/intel-sycl-gpu/build/bin/clang -cc1 -internal-isystem /home/test-user/llvm-buildbot-worker/intel-sycl-gpu/build/lib/clang/23/include -nostdsysteminc -triple riscv32 -target-feature +zihintntl -E -dM /home/test-user/llvm-buildbot-worker/intel-sycl-gpu/llvm-project/clang/test/Preprocessor/riscv-intrinsic-exts.c -o -    | /home/test-user/llvm-buildbot-worker/intel-sycl-gpu/build/bin/FileCheck --check-prefix=CHECK-INTRINSIC-EXTS /home/test-user/llvm-buildbot-worker/intel-sycl-gpu/llvm-project/clang/test/Preprocessor/riscv-intrinsic-exts.c
# executed command: /home/test-user/llvm-buildbot-worker/intel-sycl-gpu/build/bin/clang -cc1 -internal-isystem /home/test-user/llvm-buildbot-worker/intel-sycl-gpu/build/lib/clang/23/include -nostdsysteminc -triple riscv32 -target-feature +zihintntl -E -dM /home/test-user/llvm-buildbot-worker/intel-sycl-gpu/llvm-project/clang/test/Preprocessor/riscv-intrinsic-exts.c -o -
# .---command stderr------------
# | /home/test-user/llvm-buildbot-worker/intel-sycl-gpu/llvm-project/clang/test/Preprocessor/riscv-intrinsic-exts.c:16:10: fatal error: 'riscv_vector.h' file not found
# |    16 | #include <riscv_vector.h>
# |       |          ^~~~~~~~~~~~~~~~
# | 1 error generated.
# `-----------------------------
# error: command failed with exit status: 1
# executed command: /home/test-user/llvm-buildbot-worker/intel-sycl-gpu/build/bin/FileCheck --check-prefix=CHECK-INTRINSIC-EXTS /home/test-user/llvm-buildbot-worker/intel-sycl-gpu/llvm-project/clang/test/Preprocessor/riscv-intrinsic-exts.c
# .---command stderr------------
# | /home/test-user/llvm-buildbot-worker/intel-sycl-gpu/llvm-project/clang/test/Preprocessor/riscv-intrinsic-exts.c:20:26: error: CHECK-INTRINSIC-EXTS: expected string not found in input
# | // CHECK-INTRINSIC-EXTS: #define __riscv_intrinsic_v 1
# |                          ^
# | <stdin>:1:1: note: scanning from here
# | #define INT16_C(v) __INT16_C(v)
# | ^
# | <stdin>:75:1: note: possible intended match here
# | #define __BOOL_WIDTH__ 1
# | ^
# | 
# | Input file: <stdin>
# | Check file: /home/test-user/llvm-buildbot-worker/intel-sycl-gpu/llvm-project/clang/test/Preprocessor/riscv-intrinsic-exts.c
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |             1: #define INT16_C(v) __INT16_C(v) 
# | check:20'0     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
# |             2: #define INT16_MAX INT16_C(32767) 
# | check:20'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# |             3: #define INT16_MIN (-INT16_C(32767)-1) 
# | check:20'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# |             4: #define INT32_C(v) __INT32_C(v) 
# | check:20'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# |             5: #define INT32_MAX INT32_C(2147483647) 
# | check:20'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# |             6: #define INT32_MIN (-INT32_C(2147483647)-1) 
# | check:20'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# |             .
# |             .
# |             .
# |            70: #define __ATOMIC_RELAXED 0 
...

```

</details>

https://github.com/llvm/llvm-project/pull/187197