sha256: fix compilation on efi-ia32

/usr/bin/gcc -c ../src/fundamental/sha256.c -o src/boot/efi/sha256.c.o -Wno-format-signedness -Wno-missing-field-initializers -Wno-unused-parameter -Wdate-time -Wendif-labels -Werror=format=2 -Werror=implicit-function-declaration -Werror=incompatible-pointer-types -Werror=int-conversion -Werror=overflow -Werror=override-init -Werror=return-type -Werror=shift-count-overflow -Werror=shift-overflow=2 -Werror=undef -Wfloat-equal -Wimplicit-fallthrough=5 -Winit-self -Wlogical-op -Wmissing-include-dirs -Wmissing-noreturn -Wnested-externs -Wold-style-definition -Wpointer-arith -Wredundant-decls -Wshadow -Wstrict-aliasing=2 -Wstrict-prototypes -Wsuggest-attribute=noreturn -Wunused-function -Wwrite-strings -Wno-unused-result -fno-stack-protector -fno-strict-aliasing -fpic -fwide-exec-charset=UCS2 -Wall -Wextra -Wsign-compare -nostdlib -std=gnu99 -ffreestanding -fshort-wchar -fvisibility=hidden -isystem /usr/include/efi -isystem /usr/include/efi/ia32 -I /builddir/build/BUILD/systemd-stable-250.7/src/fundamental -DSD_BOOT -DGNU_EFI_USE_MS_ABI -include src/boot/efi/efi_config.h -include version.h -mno-sse -mno-mmx -flto -O2 -flto=auto
../src/fundamental/sha256.c: In function ‘sha256_finish_ctx’:
../src/fundamental/sha256.c:61:25: error: ‘false’ undeclared (first use in this function)
   61 | # define UNALIGNED_P(p) false
      |                         ^~~~~
../src/fundamental/sha256.c:136:21: note: in expansion of macro ‘UNALIGNED_P’
  136 |                 if (UNALIGNED_P(resbuf))
      |                     ^~~~~~~~~~~
../src/fundamental/sha256.c:32:1: note: ‘false’ is defined in header ‘<stdbool.h>’; did you forget to ‘#include <stdbool.h>’?
   31 | #include "sha256.h"
  +++ |+#include <stdbool.h>
   32 |
...

src/fundamental/sha256.c

@@ -60,7 +60,7 @@
 #  define UNALIGNED_P(p) (((size_t) p) % sizeof(uint32_t) != 0)
 # endif
 #else
-# define UNALIGNED_P(p) false
+# define UNALIGNED_P(p) sd_false
 #endif
 
 /* This array contains the bytes used to pad the buffer to the next