Cleanup code after dropping ICC support in favor of ICX

The commit removes all uses of ICC's __INTEL_COMPILER macro and other
references to ICC. It also adds ICX info to the compiler command and
fixes two typos in Makefile's help output.

closes #4769

No functional change

src/Makefile

@@ -804,8 +804,8 @@ help:
 	@echo ""
 	@echo "Supported compilers:"
 	@echo ""
-	@echo "gcc                     > Gnu compiler (default)"
-	@echo "mingw                   > Gnu compiler with MinGW under Windows"
+	@echo "gcc                     > GNU compiler (default)"
+	@echo "mingw                   > GNU compiler with MinGW under Windows"
 	@echo "clang                   > LLVM Clang compiler"
 	@echo "icx                     > Intel oneAPI DPC++/C++ Compiler"
 	@echo "ndk                     > Google NDK to cross-compile for Android"

src/bitboard.h

@@ -262,7 +262,7 @@ inline int popcount(Bitboard b) {
   union { Bitboard bb; uint16_t u[4]; } v = { b };
   return PopCnt16[v.u[0]] + PopCnt16[v.u[1]] + PopCnt16[v.u[2]] + PopCnt16[v.u[3]];
 
-#elif defined(_MSC_VER) || defined(__INTEL_COMPILER)
+#elif defined(_MSC_VER)
 
   return (int)_mm_popcnt_u64(b);
 
@@ -276,7 +276,7 @@ inline int popcount(Bitboard b) {
 
 /// lsb() and msb() return the least/most significant bit in a non-zero bitboard
 
-#if defined(__GNUC__)  // GCC, Clang, ICC
+#if defined(__GNUC__)  // GCC, Clang, ICX
 
 inline Square lsb(Bitboard b) {
   assert(b);

src/misc.cpp

@@ -193,22 +193,21 @@ std::string compiler_info() {
 
 /// Predefined macros hell:
 ///
-/// __GNUC__           Compiler is gcc, Clang or Intel on Linux
-/// __INTEL_COMPILER   Compiler is Intel
-/// _MSC_VER           Compiler is MSVC or Intel on Windows
-/// _WIN32             Building on Windows (any)
-/// _WIN64             Building on Windows 64 bit
+/// __GNUC__                Compiler is GCC, Clang or ICX
+/// __clang__               Compiler is Clang or ICX
+/// __INTEL_LLVM_COMPILER   Compiler is ICX
+/// _MSC_VER                Compiler is MSVC
+/// _WIN32                  Building on Windows (any)
+/// _WIN64                  Building on Windows 64 bit
 
   std::string compiler = "\nCompiled by ";
 
-  #ifdef __clang__
+  #if defined(__INTEL_LLVM_COMPILER)
+     compiler += "ICX ";
+     compiler += stringify(__INTEL_LLVM_COMPILER);
+  #elif defined(__clang__)
      compiler += "clang++ ";
      compiler += make_version_string(__clang_major__, __clang_minor__, __clang_patchlevel__);
-  #elif __INTEL_COMPILER
-     compiler += "Intel compiler ";
-     compiler += "(version ";
-     compiler += stringify(__INTEL_COMPILER) " update " stringify(__INTEL_COMPILER_UPDATE);
-     compiler += ")";
   #elif _MSC_VER
      compiler += "MSVC ";
      compiler += "(version ";
@@ -425,13 +424,7 @@ void prefetch(void*) {}
 
 void prefetch(void* addr) {
 
-#  if defined(__INTEL_COMPILER)
-   // This hack prevents prefetches from being optimized away by
-   // Intel compiler. Both MSVC and gcc seem not be affected by this.
-   __asm__ ("");
-#  endif
-
-#  if defined(__INTEL_COMPILER) || defined(_MSC_VER)
+#  if defined(_MSC_VER)
   _mm_prefetch((char*)addr, _MM_HINT_T0);
 #  else
   __builtin_prefetch(addr);

src/types.h

@@ -48,11 +48,12 @@
 
 /// Predefined macros hell:
 ///
-/// __GNUC__           Compiler is gcc, Clang or Intel on Linux
-/// __INTEL_COMPILER   Compiler is Intel
-/// _MSC_VER           Compiler is MSVC or Intel on Windows
-/// _WIN32             Building on Windows (any)
-/// _WIN64             Building on Windows 64 bit
+/// __GNUC__                Compiler is GCC, Clang or ICX
+/// __clang__               Compiler is Clang or ICX
+/// __INTEL_LLVM_COMPILER   Compiler is ICX
+/// _MSC_VER                Compiler is MSVC
+/// _WIN32                  Building on Windows (any)
+/// _WIN64                  Building on Windows 64 bit
 
 #if defined(__GNUC__ ) && (__GNUC__ < 9 || (__GNUC__ == 9 && __GNUC_MINOR__ <= 2)) && defined(_WIN32) && !defined(__clang__)
 #define ALIGNAS_ON_STACK_VARIABLES_BROKEN
@@ -65,12 +66,12 @@
 #  define IS_64BIT
 #endif
 
-#if defined(USE_POPCNT) && (defined(__INTEL_COMPILER) || defined(_MSC_VER))
-#  include <nmmintrin.h> // Intel and Microsoft header for _mm_popcnt_u64()
+#if defined(USE_POPCNT) && defined(_MSC_VER)
+#  include <nmmintrin.h> // Microsoft header for _mm_popcnt_u64()
 #endif
 
-#if !defined(NO_PREFETCH) && (defined(__INTEL_COMPILER) || defined(_MSC_VER))
-#  include <xmmintrin.h> // Intel and Microsoft header for _mm_prefetch()
+#if !defined(NO_PREFETCH) && defined(_MSC_VER)
+#  include <xmmintrin.h> // Microsoft header for _mm_prefetch()
 #endif
 
 #if defined(USE_PEXT)