Neon: Disable some strict compiler warnings

We use a standard set of strict compiler warnings with Clang and GCC to
continuously test and maintain C89 conformance in the libjpeg API code.
However, SIMD extensions need not comply with that.  The Neon code
specifically uses some C99isms, so disable
-Wdeclaration-after-statement, -Wc99-extensions, and -Wpedantic in the
scope of that code.  Also modify the Neon feature tests so that they
will succeed if any of the aforementioned compiler warnings are enabled.

simd/CMakeLists.txt

@@ -270,48 +270,33 @@ endif()
 check_c_source_compiles("
   #include <arm_neon.h>
   int main(int argc, char **argv) {
-    int16_t input[] = {
-      (int16_t)argc, (int16_t)argc, (int16_t)argc, (int16_t)argc,
-      (int16_t)argc, (int16_t)argc, (int16_t)argc, (int16_t)argc,
-      (int16_t)argc, (int16_t)argc, (int16_t)argc, (int16_t)argc
-    };
-    int16x4x3_t output = vld1_s16_x3(input);
+    int16_t input[12];
+    int16x4x3_t output;
+    int i;
+    for (i = 0; i < 12; i++) input[i] = (int16_t)argc;
+    output = vld1_s16_x3(input);
     vst3_s16(input, output);
     return (int)input[0];
   }" HAVE_VLD1_S16_X3)
 check_c_source_compiles("
   #include <arm_neon.h>
   int main(int argc, char **argv) {
-    uint16_t input[] = {
-      (uint16_t)argc, (uint16_t)argc, (uint16_t)argc, (uint16_t)argc,
-      (uint16_t)argc, (uint16_t)argc, (uint16_t)argc, (uint16_t)argc
-    };
-    uint16x4x2_t output = vld1_u16_x2(input);
+    uint16_t input[8];
+    uint16x4x2_t output;
+    int i;
+    for (i = 0; i < 8; i++) input[i] = (uint16_t)argc;
+    output = vld1_u16_x2(input);
     vst2_u16(input, output);
     return (int)input[0];
   }" HAVE_VLD1_U16_X2)
 check_c_source_compiles("
   #include <arm_neon.h>
   int main(int argc, char **argv) {
-    uint8_t input[] = {
-      (uint8_t)argc, (uint8_t)argc, (uint8_t)argc, (uint8_t)argc,
-      (uint8_t)argc, (uint8_t)argc, (uint8_t)argc, (uint8_t)argc,
-      (uint8_t)argc, (uint8_t)argc, (uint8_t)argc, (uint8_t)argc,
-      (uint8_t)argc, (uint8_t)argc, (uint8_t)argc, (uint8_t)argc,
-      (uint8_t)argc, (uint8_t)argc, (uint8_t)argc, (uint8_t)argc,
-      (uint8_t)argc, (uint8_t)argc, (uint8_t)argc, (uint8_t)argc,
-      (uint8_t)argc, (uint8_t)argc, (uint8_t)argc, (uint8_t)argc,
-      (uint8_t)argc, (uint8_t)argc, (uint8_t)argc, (uint8_t)argc,
-      (uint8_t)argc, (uint8_t)argc, (uint8_t)argc, (uint8_t)argc,
-      (uint8_t)argc, (uint8_t)argc, (uint8_t)argc, (uint8_t)argc,
-      (uint8_t)argc, (uint8_t)argc, (uint8_t)argc, (uint8_t)argc,
-      (uint8_t)argc, (uint8_t)argc, (uint8_t)argc, (uint8_t)argc,
-      (uint8_t)argc, (uint8_t)argc, (uint8_t)argc, (uint8_t)argc,
-      (uint8_t)argc, (uint8_t)argc, (uint8_t)argc, (uint8_t)argc,
-      (uint8_t)argc, (uint8_t)argc, (uint8_t)argc, (uint8_t)argc,
-      (uint8_t)argc, (uint8_t)argc, (uint8_t)argc, (uint8_t)argc
-    };
-    uint8x16x4_t output = vld1q_u8_x4(input);
+    uint8_t input[64];
+    uint8x16x4_t output;
+    int i;
+    for (i = 0; i < 64; i++) input[i] = (uint8_t)argc;
+    output = vld1q_u8_x4(input);
     vst4q_u8(input, output);
     return (int)input[0];
   }" HAVE_VLD1Q_U8_X4)

simd/arm/jcgray-neon.c

@@ -28,6 +28,7 @@
 #include "../../jsimddct.h"
 #include "../jsimd.h"
 #include "align.h"
+#include "neon-compat.h"
 
 #include <arm_neon.h>
 

simd/arm/jcsample-neon.c

@@ -28,6 +28,7 @@
 #include "../../jsimddct.h"
 #include "../jsimd.h"
 #include "align.h"
+#include "neon-compat.h"
 
 #include <arm_neon.h>
 

simd/arm/jdcolor-neon.c

@@ -28,6 +28,7 @@
 #include "../../jsimddct.h"
 #include "../jsimd.h"
 #include "align.h"
+#include "neon-compat.h"
 
 #include <arm_neon.h>
 

simd/arm/jdmerge-neon.c

@@ -28,6 +28,7 @@
 #include "../../jsimddct.h"
 #include "../jsimd.h"
 #include "align.h"
+#include "neon-compat.h"
 
 #include <arm_neon.h>
 

simd/arm/jdsample-neon.c

@@ -28,6 +28,7 @@
 #include "../../jdct.h"
 #include "../../jsimddct.h"
 #include "../jsimd.h"
+#include "neon-compat.h"
 
 #include <arm_neon.h>
 

simd/arm/jfdctfst-neon.c

@@ -28,6 +28,7 @@
 #include "../../jsimddct.h"
 #include "../jsimd.h"
 #include "align.h"
+#include "neon-compat.h"
 
 #include <arm_neon.h>
 

simd/arm/jidctfst-neon.c

@@ -28,6 +28,7 @@
 #include "../../jsimddct.h"
 #include "../jsimd.h"
 #include "align.h"
+#include "neon-compat.h"
 
 #include <arm_neon.h>
 

simd/arm/jquanti-neon.c

@@ -27,6 +27,7 @@
 #include "../../jdct.h"
 #include "../../jsimddct.h"
 #include "../jsimd.h"
+#include "neon-compat.h"
 
 #include <arm_neon.h>
 

simd/arm/neon-compat.h.in

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2020, D. R. Commander.  All Rights Reserved.
+ * Copyright (C) 2020, 2024, D. R. Commander.  All Rights Reserved.
  * Copyright (C) 2020-2021, Arm Limited.  All Rights Reserved.
  *
  * This software is provided 'as-is', without any express or implied
@@ -35,3 +35,11 @@
 #else
 #error "Unknown compiler"
 #endif
+
+#if defined(__clang__)
+#pragma clang diagnostic ignored "-Wdeclaration-after-statement"
+#pragma clang diagnostic ignored "-Wc99-extensions"
+#elif defined(__GNUC__)
+#pragma GCC diagnostic ignored "-Wdeclaration-after-statement"
+#pragma GCC diagnostic ignored "-Wpedantic"
+#endif