[SYCL-JIT][NFCI] Enable few extra warnings (#19118)

Those extra flags are required per our internal guidelines (the full
list you can find in `llvm/cmake/modules/AddSecurityFlags.cmake`.

Even though we have this shared cmake module that applies those flags, I
don't think that we will be able to use it for every flag, because
baseline LLVM that we use isn't warning-free. Therefore, those flags
were directly applied to `sycl-jit`.

Author: AlexeySachkov

sycl-jit/CMakeLists.txt

@@ -11,7 +11,7 @@ set(LLVM_SPIRV_INCLUDE_DIRS "${LLVM_MAIN_SRC_DIR}/../llvm-spirv/include")
 
 if (NOT WIN32 AND NOT CYGWIN)
   # Set library-wide warning options.
-  set(SYCL_JIT_WARNING_FLAGS -Wall -Wextra)
+  set(SYCL_JIT_WARNING_FLAGS -Wall -Wextra -Wconversion -Wimplicit-fallthrough)
 
   option(SYCL_JIT_ENABLE_WERROR "Treat all warnings as errors in SYCL JIT library" ON)
   if(SYCL_JIT_ENABLE_WERROR)

sycl-jit/jit-compiler/include/DynArray.h

@@ -10,6 +10,7 @@
 
 #include <algorithm>
 #include <cstring>
+#include <iterator>
 
 namespace jit_compiler {
 
@@ -22,7 +23,7 @@ template <typename T> class DynArray {
   explicit DynArray(size_t Size) { init(Size); }
 
   template <typename InputIt> DynArray(InputIt Begin, InputIt End) {
-    init(End - Begin);
+    init(static_cast<size_t>(End - Begin));
     std::copy(Begin, End, this->begin());
   }
 

sycl-jit/jit-compiler/lib/rtc/RTC.cpp

@@ -71,7 +71,7 @@ JIT_EXPORT_SYMBOL RTCResult compileSYCL(InMemoryFile SourceFile,
   if (auto *Arg =
           UserArgList.getLastArg(clang::driver::options::OPT_ftime_trace_EQ)) {
     TraceFileName = Arg->getValue();
-    int Granularity =
+    unsigned Granularity =
         500; // microseconds. Same default as in `clang::FrontendOptions`.
     if (auto *Arg = UserArgList.getLastArg(
             clang::driver::options::OPT_ftime_trace_granularity_EQ)) {