[clang-tidy] Remove some test c++ mode restrictions.

[njames93]

Summary

Some comments are redundant, others just simple fixes.

[aaron.ballman]

LGTM!

clang-tools-extra/test/clang-tidy/checkers/abseil-faster-strsplit-delimiter.cpp

 // RUN: %check_clang_tidy -std=c++11-or-later %s abseil-faster-strsplit-delimiter %t
-// FIXME: Fix the checker to work in C++17 mode.
 
 namespace absl {
 
 class string_view {
   public:
     string_view();
     string_view(const char *);
 };

clang-tools-extra/test/clang-tidy/checkers/abseil-time-subtraction.cpp

 // RUN: %check_clang_tidy -std=c++11-or-later %s abseil-time-subtraction %t -- -- -I %S/Inputs
-// FIXME: Fix the checker to work in C++17 mode.
 
 #include "absl/time/time.h"
 
 void g(absl::Duration d);
 
 void f() {
   absl::Time t;
   int x, y;

clang-tools-extra/test/clang-tidy/checkers/abseil-upgrade-duration-conversions.cpp

 // RUN: %check_clang_tidy -std=c++11-or-later %s abseil-upgrade-duration-conversions %t -- -- -I%S/Inputs
-// FIXME: Fix the checker to work in C++17 mode.
 
 using int64_t = long long;
 
 #include "absl/time/time.h"
 
 template <typename T> struct ConvertibleTo {
   operator T() const;
 };

clang-tools-extra/test/clang-tidy/checkers/google-readability-casting.cpp

 // RUN: %check_clang_tidy -std=c++11-or-later %s google-readability-casting %t
-// FIXME: Fix the checker to work in C++17 mode.
 
 bool g() { return false; }
 
 enum Enum { Enum1 };
 struct X {};
 struct Y : public X {};
 
 void f(int a, double b, const char *cpc, const void *cpv, X *pX) {

clang-tools-extra/test/clang-tidy/checkers/portability-simd-intrinsics-ppc.cpp

 // RUN: %check_clang_tidy -std=c++11,c++14,c++17 %s portability-simd-intrinsics %t -- \
 // RUN:  -config='{CheckOptions: [ \
 // RUN:    {key: portability-simd-intrinsics.Suggest, value: 1} \
 // RUN:  ]}' -- -target ppc64le -maltivec
-// FIXME: Fix the checker to work in C++20 mode.
+// RUN: %check_clang_tidy -std=c++20-or-later %s portability-simd-intrinsics -check-suffix=CXX20 %t -- \
+// RUN:  -config='{CheckOptions: [ \
+// RUN:    {key: portability-simd-intrinsics.Suggest, value: 1} \
+// RUN:  ]}' -- -target ppc64le -maltivec
 
 vector int vec_add(vector int, vector int);
 
 void PPC() {
   vector int i0, i1;
 
   vec_add(i0, i1);
   // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: 'vec_add' can be replaced by operator+ on std::experimental::simd objects [portability-simd-intrinsics]
+  // CHECK-MESSAGES-CXX20: :[[@LINE-2]]:3: warning: 'vec_add' can be replaced by operator+ on std::simd objects [portability-simd-intrinsics]
 }

clang-tools-extra/test/clang-tidy/checkers/portability-simd-intrinsics-x86.cpp

 // RUN: %check_clang_tidy -std=c++11,c++14,c++17 %s portability-simd-intrinsics %t -- \
 // RUN:  -config='{CheckOptions: [ \
 // RUN:    {key: portability-simd-intrinsics.Suggest, value: 1} \
 // RUN:  ]}' -- -target x86_64
-// FIXME: Fix the checker to work in C++20 mode.
+// RUN: %check_clang_tidy -std=c++20-or-later %s portability-simd-intrinsics -check-suffix=CXX20 %t -- \
+// RUN:  -config='{CheckOptions: [ \
+// RUN:    {key: portability-simd-intrinsics.Suggest, value: 1} \
+// RUN:  ]}' -- -target x86_64
 
 typedef long long __m128i __attribute__((vector_size(16)));
 typedef double __m256 __attribute__((vector_size(32)));
 
 __m128i _mm_add_epi32(__m128i, __m128i);
 __m256 _mm256_load_pd(double const *);
 void _mm256_store_pd(double *, __m256);
 
 int _mm_add_fake(int, int);
 
 void X86() {
   __m128i i0, i1;
   __m256 d0;
 
   _mm_add_epi32(i0, i1);
   // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: '_mm_add_epi32' can be replaced by operator+ on std::experimental::simd objects [portability-simd-intrinsics]
+  // CHECK-MESSAGES-CXX20: :[[@LINE-2]]:3: warning: '_mm_add_epi32' can be replaced by operator+ on std::simd objects [portability-simd-intrinsics]
   d0 = _mm256_load_pd(0);
   _mm256_store_pd(0, d0);
 
   _mm_add_fake(0, 1);
 }