AK+Everywhere: Add AK_COMPILER_{GCC,CLANG} and use them most places

Doesn't use them in libc headers so that those don't have to pull in
AK/Platform.h.

AK_COMPILER_GCC is set _only_ for gcc, not for clang too. (__GNUC__ is
defined in clang builds as well.) Using AK_COMPILER_GCC simplifies
things some.

AK_COMPILER_CLANG isn't as much of a win, other than that it's
consistent with AK_COMPILER_GCC.

Userland/Libraries/LibC/arch/x86_64/memset.cpp

@@ -41,7 +41,7 @@ namespace {
 }
 }
 
-#if !defined(__clang__) && !defined(_DYNAMIC_LOADER)
+#if !defined(AK_COMPILER_CLANG) && !defined(_DYNAMIC_LOADER)
 [[gnu::ifunc("resolve_memset")]] void* memset(void*, int, size_t);
 #else
 // DynamicLoader can't self-relocate IFUNCs.

Userland/Libraries/LibC/math.cpp

@@ -19,7 +19,7 @@
 #include <stdint.h>
 #include <stdlib.h>
 
-#ifdef __clang__
+#if defined(AK_COMPILER_CLANG)
 #    pragma clang diagnostic push
 #    pragma clang diagnostic ignored "-Wdouble-promotion"
 #endif
@@ -1148,6 +1148,6 @@ float nearbyintf(float value) NOEXCEPT
 }
 }
 
-#ifdef __clang__
+#if defined(AK_COMPILER_CLANG)
 #    pragma clang diagnostic pop
 #endif

Userland/Libraries/LibDebug/Dwarf/DwarfInfo.cpp

@@ -64,7 +64,7 @@ void DwarfInfo::populate_compilation_units()
         // HACK: Clang generates line programs for embedded resource assembly files, but not compile units.
         // Meaning that for graphical applications, some line info data would be unread, triggering the assertion below.
         // As a fix, we don't create compilation units for line programs that come from resource files.
-#ifdef __clang__
+#if defined(AK_COMPILER_CLANG)
         if (line_program->source_files().size() == 1 && line_program->source_files()[0].name.view().contains("serenity_icon_"sv)) {
             debug_info_stream.seek(unit_offset);
         } else

Userland/Libraries/LibEDID/EDID.cpp

@@ -23,7 +23,7 @@ namespace EDID {
 
 // clang doesn't like passing around pointers to members in packed structures,
 // even though we're only using them for arithmetic purposes
-#ifdef __clang__
+#if defined(AK_COMPILER_CLANG)
 #    pragma clang diagnostic ignored "-Waddress-of-packed-member"
 #endif
 

Userland/Libraries/LibGfx/AntiAliasingPainter.cpp

@@ -5,7 +5,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#if defined(__GNUC__) && !defined(__clang__)
+#if defined(AK_COMPILER_GCC)
 #    pragma GCC optimize("O3")
 #endif
 

Userland/Libraries/LibGfx/Filters/FastBoxBlurFilter.cpp

@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#if defined(__GNUC__) && !defined(__clang__)
+#if defined(AK_COMPILER_GCC)
 #    pragma GCC optimize("O3")
 #endif
 

Userland/Libraries/LibGfx/Filters/StackBlurFilter.cpp

@@ -5,7 +5,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#if defined(__GNUC__) && !defined(__clang__)
+#if defined(AK_COMPILER_GCC)
 #    pragma GCC optimize("O3")
 #endif
 

Userland/Libraries/LibGfx/Painter.cpp

@@ -36,7 +36,7 @@
 #include <LibGfx/TextLayout.h>
 #include <stdio.h>
 
-#if defined(__GNUC__) && !defined(__clang__)
+#if defined(AK_COMPILER_GCC)
 #    pragma GCC optimize("O3")
 #endif
 

Userland/Libraries/LibGfx/VectorN.h

@@ -21,7 +21,7 @@
 #define STRINGIFY_HELPER(x) #x
 #define STRINGIFY(x) STRINGIFY_HELPER(x)
 
-#ifdef __clang__
+#if defined(AK_COMPILER_CLANG)
 #    define UNROLL_LOOP _Pragma(STRINGIFY(unroll))
 #else
 #    define UNROLL_LOOP _Pragma(STRINGIFY(GCC unroll(LOOP_UNROLL_N)))

Userland/Libraries/LibJS/Runtime/NumberConstructor.cpp

@@ -11,7 +11,7 @@
 #include <LibJS/Runtime/NumberConstructor.h>
 #include <LibJS/Runtime/NumberObject.h>
 
-#ifdef __clang__
+#if defined(AK_COMPILER_CLANG)
 #    define EPSILON_VALUE AK::exp2(-52.)
 #    define MAX_SAFE_INTEGER_VALUE AK::exp2(53.) - 1
 #    define MIN_SAFE_INTEGER_VALUE -(AK::exp2(53.) - 1)

Userland/Libraries/LibX86/Instruction.cpp

@@ -8,7 +8,7 @@
 #include <LibX86/Instruction.h>
 #include <LibX86/Interpreter.h>
 
-#if defined(__GNUC__) && !defined(__clang__)
+#if defined(AK_COMPILER_GCC)
 #    pragma GCC optimize("O3")
 #endif