clar/sandbox: convert to use clar_abort()

The function `clar_sandbox()` can fail either because it failed to build
a sandbox path or because it failed to change directories into it. The
error reporting happens at the callsite of this function though, where
we are unable to distinguish those two root causes.

Adapt the code to instead perform error handling via `clar_abort()` in
`clar_sandbox()` itself. This gives us direct access to the root cause.
Callers do not need to check for errors anymore.

clar.c

@@ -189,7 +189,7 @@ static void clar_print_onabort(const char *msg, ...);
 
 /* From clar_sandbox.c */
 static void clar_unsandbox(void);
-static int clar_sandbox(void);
+static void clar_sandbox(void);
 
 /* From summary.h */
 static struct clar_summary *clar_summary_init(const char *filename);
@@ -570,8 +570,7 @@ clar_test_init(int argc, char **argv)
 	if (_clar.write_summary)
 	    _clar.summary = clar_summary_init(_clar.summary_filename);
 
-	if (clar_sandbox() < 0)
-		clar_abort("Failed to sandbox the test runner.\n");
+	clar_sandbox();
 }
 
 int

clar/sandbox.h

@@ -142,15 +142,14 @@ static int build_sandbox_path(void)
 	return 0;
 }
 
-static int clar_sandbox(void)
+static void clar_sandbox(void)
 {
 	if (_clar_path[0] == '\0' && build_sandbox_path() < 0)
-		return -1;
+		clar_abort("Failed to build sandbox path.\n");
 
 	if (chdir(_clar_path) != 0)
-		return -1;
-
-	return 0;
+		clar_abort("Failed to change into sandbox directory '%s': %s.\n",
+			   _clar_path, strerror(errno));
 }
 
 const char *clar_sandbox_path(void)