Use cmake to find perl executable (#91275)

`clang/tools/scan-build` is implemented in `perl`. However given `perl`
is not mentioned as a required dependency in `GettingStarted.rst` we
should make this optional.

This adds a `find_package(Perl)` check to cmake and disables the
`scan-build` tests when no perl executable is found.

Ideally we would also check if dependent perl modules like `Hash::Util`
are present on the system, but I don't see any pre-existing cmake macros
to easily test this. So for now I go with a plain check for the `perl`
package, at least this allows to use `cmake
-DCMAKE_DISABLE_FIND_PACKAGE_Perl=ON` to manually disable `perl` and the
tests.

Author: MatzeB

clang/CMakeLists.txt

@@ -523,6 +523,8 @@ endif()
 
 
 if( CLANG_INCLUDE_TESTS )
+  find_package(Perl)
+
   add_subdirectory(unittests)
   list(APPEND CLANG_TEST_DEPS ClangUnitTests)
   list(APPEND CLANG_TEST_PARAMS

clang/test/Analysis/scan-build/deduplication.test

@@ -1,4 +1,3 @@
-// FIXME: Actually, "perl".
 REQUIRES: shell
 
 RUN: rm -rf %t.output_dir && mkdir %t.output_dir

clang/test/Analysis/scan-build/exclude_directories.test

@@ -1,6 +1,3 @@
-// FIXME: Actually, "perl".
-REQUIRES: shell
-
 RUN: rm -rf %t.output_dir && mkdir %t.output_dir
 RUN: %scan-build -o %t.output_dir %clang -S \
 RUN:     %S/Inputs/multidirectory_project/directory1/file1.c \

clang/test/Analysis/scan-build/help.test

@@ -1,6 +1,3 @@
-// FIXME: Actually, "perl".
-REQUIRES: shell
-
 RUN: %scan-build -h | FileCheck %s
 RUN: %scan-build --help | FileCheck %s
 

clang/test/Analysis/scan-build/html_output.test

@@ -1,4 +1,3 @@
-// FIXME: Actually, "perl".
 REQUIRES: shell
 
 RUN: rm -rf %t.output_dir && mkdir %t.output_dir

clang/test/Analysis/scan-build/lit.local.cfg

@@ -1,8 +1,8 @@
 # -*- Python -*-
 
-import lit.util
 import lit.formats
 import os
+import platform
 
 use_lit_shell = os.environ.get("LIT_USE_INTERNAL_SHELL")
 config.test_format = lit.formats.ShTest(use_lit_shell == "0")
@@ -12,13 +12,16 @@ clang_path = config.clang if config.have_llvm_driver else os.path.realpath(confi
 config.substitutions.append(
     (
         "%scan-build",
-        "'%s' --use-analyzer=%s "
+        "'%s' '%s' --use-analyzer=%s "
         % (
-            lit.util.which(
-                "scan-build",
-                os.path.join(config.clang_src_dir, "tools", "scan-build", "bin"),
+            config.perl_executable,
+            os.path.join(
+                config.clang_src_dir, "tools", "scan-build", "bin", "scan-build"
             ),
             clang_path,
         ),
     )
 )
+
+if not config.perl_executable or platform.system() == "Windows":
+    config.unsupported = True

clang/test/Analysis/scan-build/plist_html_output.test

@@ -1,4 +1,3 @@
-// FIXME: Actually, "perl".
 REQUIRES: shell
 
 RUN: rm -rf %t.output_dir && mkdir %t.output_dir

clang/test/Analysis/scan-build/plist_output.test

@@ -1,4 +1,3 @@
-// FIXME: Actually, "perl".
 REQUIRES: shell
 
 RUN: rm -rf %t.output_dir && mkdir %t.output_dir

clang/test/Analysis/scan-build/rebuild_index/rebuild_index.test

@@ -1,6 +1,3 @@
-// FIXME: Actually, "perl".
-REQUIRES: shell
-
 RUN: rm -rf %t.output_dir && mkdir %t.output_dir
 RUN: cp %S/report-1.html %t.output_dir
 RUN: cp %S/report-2.html %t.output_dir

clang/test/Analysis/scan-build/silence-core-checkers.test

@@ -1,6 +1,3 @@
-// FIXME: Actually, "perl".
-REQUIRES: shell
-
 RUN: rm -rf %t.output_dir && mkdir %t.output_dir
 RUN: %scan-build -o %t.output_dir \
 RUN:   %clang -S %S/Inputs/null_dereference_and_division_by_zero.c \