clover: Fix build with llvm-12.

Fix build error after LLVM commit c495dfe0268b ("[clang][cli] NFC:
Decrease the scope of ParseLangArgs parameters").

../src/gallium/frontends/clover/llvm/invocation.cpp: In function ‘std::unique_ptr<clang::CompilerInstance> {anonymous}::create_compiler_instance(const clover::device&, const string&, const std::vector<std::__cxx11::basic_string<char> >&, std::string&)’:
../src/gallium/frontends/clover/llvm/invocation.cpp:252:55: error: cannot convert ‘clang::PreprocessorOptions’ to ‘std::vector<std::__cxx11::basic_string<char> >&’
  252 |                                 c->getPreprocessorOpts(),
      |                                 ~~~~~~~~~~~~~~~~~~~~~~^~
      |                                                       |
      |                                                       clang::PreprocessorOptions

Signed-off-by: Vinson Lee <vlee@freedesktop.org>
36 jobs for !8543 with fix-clover-llvm-12 in 8 seconds (queued for 5 seconds)
detached
Status Job ID Name Coverage
  Sanity
passed #6700662
sanity

00:00:08

 
  Container
manual #6700665
aarch64 manual
arm_build
manual #6700666
manual
arm_test-base
manual #6700667
windows shell 1809 mesa manual
windows_build_vs2019
manual #6700663
manual
x86_build-base
manual #6700664
manual
x86_test-base
 
  Container 2
created #6700675
android_build
created #6700678
arm64_test
created #6700679
armhf_test
created #6700672
i386_build
created #6700668
kernel+rootfs_amd64
created #6700669
aarch64
kernel+rootfs_arm64
created #6700670
aarch64
kernel+rootfs_armhf
created #6700673
ppc64el_build
created #6700674
s390x_build
created #6700671
x86_build
created #6700676
x86_test-gl
created #6700677
x86_test-vk
 
  Meson X86 64
created #6700685
meson-clang
created #6700686
meson-clover
created #6700682
meson-clover-testing
created #6700683
meson-gallium
created #6700684
meson-release
created #6700680
meson-testing
created #6700681
meson-testing-asan
created #6700687
meson-vulkan
 
  Build Misc
created #6700688
meson-android
created #6700690
aarch64
meson-arm64
created #6700691
aarch64
meson-arm64-build-test
created #6700689
aarch64
meson-armhf
created #6700693
meson-i386
created #6700696
meson-mingw32-x86_64
created #6700695
kvm
meson-ppc64el
created #6700694
kvm
meson-s390x
created #6700692
allowed to fail
scons-win64
 
  Software Renderer
created #6700697
llvmpipe-piglit-cl