add hook for manually adding coverage data (JuliaLang#41904)

This would allow packages like JuliaInterpreter to properly report
coverage data.

src/codegen.cpp

@@ -1897,6 +1897,16 @@ static void coverageAllocLine(StringRef filename, int line)
     allocLine(coverageData[filename], line);
 }
 
+extern "C" JL_DLLEXPORT void jl_coverage_visit_line(const char* filename_, size_t len_filename, int line)
+{
+    StringRef filename = StringRef(filename_, len_filename);
+    if (imaging_mode || filename == "" || filename == "none" || filename == "no file" || filename == "<missing>" || line < 0)
+        return;
+    std::vector<logdata_block*> &vec = coverageData[filename];
+    uint64_t *ptr = allocLine(vec, line);
+    (*ptr)++;
+}
+
 // Memory allocation log (malloc_log)
 
 static logdata_t mallocData;