libpng: update to 1.2.43

third_party/libpng/pnggccrd.c

Index: third_party/libpng/pnggccrd.c
diff --git a/third_party/libpng/pnggccrd.c b/third_party/libpng/pnggccrd.c
index e61523e77a28864b0d2a0698b534bd85a7c9f71a..78b8a7e4173a19fdf617f307c3f862350d83d08c 100644
--- a/third_party/libpng/pnggccrd.c
+++ b/third_party/libpng/pnggccrd.c
@@ -17,9 +17,9 @@ int PNGAPI
 png_dummy_mmx_support(void)
 {
    int result;
-#if defined(PNG_MMX_CODE_SUPPORTED)  // superfluous, but what the heck
+#ifdef PNG_MMX_CODE_SUPPORTED  // superfluous, but what the heck
     __asm__ __volatile__ (
-#if defined(__x86_64__)
+#ifdef __x86_64__
         "pushq %%rbx          \n\t"  // rbx gets clobbered by CPUID instruction
         "pushq %%rcx          \n\t"  // so does rcx...
         "pushq %%rdx          \n\t"  // ...and rdx (but rcx & rdx safe on Linux)
@@ -71,7 +71,7 @@ png_dummy_mmx_support(void)
     "0:                       \n\t"  // .NOT_SUPPORTED: target label for jump instructions
         "movl $0, %%eax       \n\t"  // set return value to 0
     "1:                       \n\t"  // .RETURN: target label for jump instructions
-#if defined(__x86_64__)
+#ifdef __x86_64__
         "popq %%rdx           \n\t"  // restore rdx
         "popq %%rcx           \n\t"  // restore rcx
         "popq %%rbx           \n\t"  // restore rbx