tools/embed: add ELF type conversion functions

Converts the pointers in the ELF embedder state structure
to a pointer to a lone ELF structure type.

Fixes gcc build errors because unsigned char * cannot be converted
implicitly to the structure types. Both GCC and clang reject this
code as invalid when compiled in my laptop and in GitHub actions.
The clang provided by Termux doesn't complain though. Weird...

source/tools/lone-embed.c

@@ -57,6 +57,18 @@ struct elf {
 	} data;
 };
 
+static struct lone_elf_header *
+hdr(struct elf *elf)
+{
+	return (struct lone_elf_header *) elf->header.pointer;
+}
+
+static struct lone_elf_segment *
+segs(struct elf *elf)
+{
+	return (struct lone_elf_segment *) elf->header.pointer;
+}
+
 static size_t pht_size_for(struct elf *elf, size_t entry_count)
 {
 	return elf->segments.table.segment.size * entry_count;
@@ -199,7 +211,7 @@ static void validate_elf_header(struct elf *elf)
 {
 	elf->class = LONE_ELF_IDENT_CLASS_INVALID;
 
-	if (lone_elf_header_is_valid(elf->header.pointer)) {
+	if (lone_elf_header_is_valid(hdr(elf))) {
 		elf->class = elf->header.pointer[LONE_ELF_IDENT_INDEX_CLASS];
 	} else {
 		invalid_elf();
@@ -213,13 +225,13 @@ static void load_program_header_table(struct elf *elf)
 	lone_elf_umax size;
 	void *address;
 
-	offset = lone_elf_header_read_segments_offset(elf->header.pointer);
+	offset = lone_elf_header_read_segments_offset(hdr(elf));
 	if (!offset.present) { invalid_elf(); }
 
-	entry_size = lone_elf_header_read_segment_size(elf->header.pointer);
+	entry_size = lone_elf_header_read_segment_size(hdr(elf));
 	if (!entry_size.present) { invalid_elf(); }
 
-	entry_count = lone_elf_header_read_segment_count(elf->header.pointer);
+	entry_count = lone_elf_header_read_segment_count(hdr(elf));
 	if (!entry_count.present) { invalid_elf(); }
 
 	elf->segments.nulls_count = 0;
@@ -290,7 +302,7 @@ static void set_start_end(lone_elf_umax *start, lone_elf_umax *end,
 
 static void analyze(struct elf *elf)
 {
-	struct lone_elf_header *header = elf->header.pointer;
+	struct lone_elf_header *header = hdr(elf);
 	lone_u16 entry_count = elf->segments.table.segment.count;
 	struct lone_elf_segment *segment;
 	struct lone_optional_u32 type;
@@ -344,8 +356,8 @@ static void adjust_phdr_entry(struct elf *elf)
 	lone_elf_umax alignment, size, size_aligned, offset, virtual, physical;
 	lone_u32 type;
 
-	header = elf->header.pointer;
-	segments = elf->segments.table.segments;
+	header = hdr(elf);
+	segments = segs(elf);
 	entry_count = elf->segments.table.segment.count;
 	phdr = 0;
 	load = 0;