fix gcc warnings about uninitialized variables

like:

src/shared/install.c: In function ‘unit_file_lookup_state’:
src/shared/install.c:1861:16: warning: ‘r’ may be used uninitialized in
this function [-Wmaybe-uninitialized]
         return r < 0 ? r : state;
                ^
src/shared/install.c:1796:13: note: ‘r’ was declared here
         int r;
             ^

src/shared/base-filesystem.c

@@ -50,7 +50,7 @@ static const BaseFilesystem table[] = {
 int base_filesystem_create(const char *root) {
         _cleanup_close_ int fd = -1;
         unsigned i;
-        int r;
+        int r = 0;
 
         fd = open(root, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW);
         if (fd < 0)

src/shared/btrfs-util.c

@@ -717,7 +717,7 @@ int btrfs_resize_loopback_fd(int fd, uint64_t new_size, bool grow_only) {
         _cleanup_free_ char *p = NULL, *loop = NULL, *backing = NULL;
         _cleanup_close_ int loop_fd = -1, backing_fd = -1;
         struct stat st;
-        dev_t dev;
+        dev_t dev = 0;
         int r;
 
         /* btrfs cannot handle file systems < 16M, hence use this as minimum */

src/shared/capability.c

@@ -50,7 +50,7 @@ unsigned long cap_last_cap(void) {
         static thread_local unsigned long saved;
         static thread_local bool valid = false;
         _cleanup_free_ char *content = NULL;
-        unsigned long p;
+        unsigned long p = 0;
         int r;
 
         if (valid)

src/shared/copy.c

@@ -360,7 +360,7 @@ int copy_file_fd(const char *from, int fdt, bool try_reflink) {
 }
 
 int copy_file(const char *from, const char *to, int flags, mode_t mode, unsigned chattr_flags) {
-        int fdt, r;
+        int fdt = -1, r;
 
         assert(from);
         assert(to);
@@ -390,7 +390,7 @@ int copy_file(const char *from, const char *to, int flags, mode_t mode, unsigned
 }
 
 int copy_file_atomic(const char *from, const char *to, mode_t mode, bool replace, unsigned chattr_flags) {
-        _cleanup_free_ char *t;
+        _cleanup_free_ char *t = NULL;
         int r;
 
         assert(from);
@@ -421,7 +421,7 @@ int copy_file_atomic(const char *from, const char *to, mode_t mode, bool replace
 int copy_times(int fdf, int fdt) {
         struct timespec ut[2];
         struct stat st;
-        usec_t crtime;
+        usec_t crtime = 0;
 
         assert(fdf >= 0);
         assert(fdt >= 0);

src/shared/install.c

@@ -1793,7 +1793,7 @@ UnitFileState unit_file_lookup_state(
         UnitFileState state = _UNIT_FILE_STATE_INVALID;
         char **i;
         _cleanup_free_ char *path = NULL;
-        int r;
+        int r = 0;
 
         assert(paths);
 

src/shared/logs-show.c

@@ -990,7 +990,7 @@ static int show_journal(FILE *f,
 
                 if (warn_cutoff && line < how_many && not_before > 0) {
                         sd_id128_t boot_id;
-                        usec_t cutoff;
+                        usec_t cutoff = 0;
 
                         /* Check whether the cutoff line is too early */
 

src/shared/util.c

@@ -2882,7 +2882,7 @@ int getttyname_malloc(int fd, char **ret) {
 
 int getttyname_harder(int fd, char **r) {
         int k;
-        char *s;
+        char *s = NULL;
 
         k = getttyname_malloc(fd, &s);
         if (k < 0)
@@ -3435,7 +3435,7 @@ char **replace_env_argv(char **argv, char **env) {
                 /* If $FOO appears as single word, replace it by the split up variable */
                 if ((*i)[0] == '$' && (*i)[1] != '{') {
                         char *e;
-                        char **w, **m;
+                        char **w, **m = NULL;
                         unsigned q;
 
                         e = strv_env_get(env, *i+1);