tree-wide: do not compile deprecated functions with hard deprecation

When compiling libgit2 with -DDEPRECATE_HARD, we add a preprocessor
definition `GIT_DEPRECATE_HARD` which causes the "git2/deprecated.h"
header to be empty. As a result, no function declarations are made
available to callers, but the implementations are still available to
link against. This has the problem that function declarations also
aren't visible to the implementations, meaning that the symbol's
visibility will not be set up correctly. As a result, the resulting
library may not expose those deprecated symbols at all on some platforms
and thus cause linking errors.

Fix the issue by conditionally compiling deprecated functions, only.
While it becomes impossible to link against such a library in case one
uses deprecated functions, distributors of libgit2 aren't expected to
pass -DDEPRECATE_HARD anyway. Instead, users of libgit2 should manually
define GIT_DEPRECATE_HARD to hide deprecated functions. Using "real"
hard deprecation still makes sense in the context of CI to test we don't
use deprecated symbols ourselves and in case a dependant uses libgit2 in
a vendored way and knows it won't ever use any of the deprecated symbols
anyway.

Author: pks-t

src/blame.c

@@ -538,7 +538,9 @@ int git_blame_options_init(git_blame_options *opts, unsigned int version)
 	return 0;
 }
 
+#ifndef GIT_DEPRECATE_HARD
 int git_blame_init_options(git_blame_options *opts, unsigned int version)
 {
 	return git_blame_options_init(opts, version);
 }
+#endif

src/blob.c

@@ -445,6 +445,7 @@ int git_blob_filter(
 
 /* Deprecated functions */
 
+#ifndef GIT_DEPRECATE_HARD
 int git_blob_create_frombuffer(
 	git_oid *id, git_repository *repo, const void *buffer, size_t len)
 {
@@ -491,3 +492,4 @@ int git_blob_filtered_content(
 
 	return git_blob_filter(out, blob, path, &opts);
 }
+#endif

src/buffer.c

@@ -133,10 +133,12 @@ void git_buf_dispose(git_buf *buf)
 	git_buf_init(buf, 0);
 }
 
+#ifndef GIT_DEPRECATE_HARD
 void git_buf_free(git_buf *buf)
 {
 	git_buf_dispose(buf);
 }
+#endif
 
 void git_buf_sanitize(git_buf *buf)
 {

src/checkout.c

@@ -2820,7 +2820,9 @@ int git_checkout_options_init(git_checkout_options *opts, unsigned int version)
 	return 0;
 }
 
+#ifndef GIT_DEPRECATE_HARD
 int git_checkout_init_options(git_checkout_options *opts, unsigned int version)
 {
 	return git_checkout_options_init(opts, version);
 }
+#endif

src/cherrypick.c

@@ -229,8 +229,10 @@ int git_cherrypick_options_init(
 	return 0;
 }
 
+#ifndef GIT_DEPRECATE_HARD
 int git_cherrypick_init_options(
 	git_cherrypick_options *opts, unsigned int version)
 {
 	return git_cherrypick_options_init(opts, version);
 }
+#endif

src/clone.c

@@ -479,10 +479,12 @@ int git_clone_options_init(git_clone_options *opts, unsigned int version)
 	return 0;
 }
 
+#ifndef GIT_DEPRECATE_HARD
 int git_clone_init_options(git_clone_options *opts, unsigned int version)
 {
 	return git_clone_options_init(opts, version);
 }
+#endif
 
 static bool can_link(const char *src, const char *dst, int link)
 {

src/describe.c

@@ -876,10 +876,12 @@ int git_describe_options_init(git_describe_options *opts, unsigned int version)
 	return 0;
 }
 
+#ifndef GIT_DEPRECATE_HARD
 int git_describe_init_options(git_describe_options *opts, unsigned int version)
 {
 	return git_describe_options_init(opts, version);
 }
+#endif
 
 int git_describe_format_options_init(git_describe_format_options *opts, unsigned int version)
 {
@@ -888,7 +890,9 @@ int git_describe_format_options_init(git_describe_format_options *opts, unsigned
 	return 0;
 }
 
+#ifndef GIT_DEPRECATE_HARD
 int git_describe_init_format_options(git_describe_format_options *opts, unsigned int version)
 {
 	return git_describe_format_options_init(opts, version);
 }
+#endif

src/diff.c

@@ -352,10 +352,12 @@ int git_diff_options_init(git_diff_options *opts, unsigned int version)
 	return 0;
 }
 
+#ifndef GIT_DEPRECATE_HARD
 int git_diff_init_options(git_diff_options *opts, unsigned int version)
 {
 	return git_diff_options_init(opts, version);
 }
+#endif
 
 int git_diff_find_options_init(
 	git_diff_find_options *opts, unsigned int version)
@@ -365,11 +367,13 @@ int git_diff_find_options_init(
 	return 0;
 }
 
+#ifndef GIT_DEPRECATE_HARD
 int git_diff_find_init_options(
 	git_diff_find_options *opts, unsigned int version)
 {
 	return git_diff_find_options_init(opts, version);
 }
+#endif
 
 int git_diff_format_email_options_init(
 	git_diff_format_email_options *opts, unsigned int version)
@@ -380,11 +384,13 @@ int git_diff_format_email_options_init(
 	return 0;
 }
 
+#ifndef GIT_DEPRECATE_HARD
 int git_diff_format_email_init_options(
 	git_diff_format_email_options *opts, unsigned int version)
 {
 	return git_diff_format_email_options_init(opts, version);
 }
+#endif
 
 static int flush_hunk(git_oid *result, git_hash_ctx *ctx)
 {

src/errors.c

@@ -210,6 +210,7 @@ void git_error_system_set(int code)
 
 /* Deprecated error values and functions */
 
+#ifndef GIT_DEPRECATE_HARD
 const git_error *giterr_last(void)
 {
 	return git_error_last();
@@ -229,3 +230,4 @@ void giterr_set_oom(void)
 {
 	git_error_set_oom();
 }
+#endif

src/fetch.c

@@ -155,7 +155,9 @@ int git_fetch_options_init(git_fetch_options *opts, unsigned int version)
 	return 0;
 }
 
+#ifndef GIT_DEPRECATE_HARD
 int git_fetch_init_options(git_fetch_options *opts, unsigned int version)
 {
 	return git_fetch_options_init(opts, version);
 }
+#endif