stacktrace: Implement is_ignored function

is_ignored function can be used to check whether the input `report` contains
any ignore string. Ignore string can be read from the given file. Each line
of the file is considered as ignore string. Ignore string could be function
name, library name as well as something you want.

Ignore file example:

  $ cat ignore.txt
  libfoo
  bar
  baz

Signed-off-by: Bojun Seo <bojun.seo.0@gmail.com>

src/stacktrace.cc

@@ -17,7 +17,6 @@
 #include <map>
 #include <sstream>
 #include <vector>
-
 #include <mutex>
 
 #include "compiler.h"
@@ -29,9 +28,40 @@
 
 std::map<stack_trace_t, stack_info_t> stackmap;
 std::map<addr_t, object_info_t> addrmap;
+std::vector<std::string> ignorevec;
+bool ignorevec_initialized = false;
 
 std::recursive_mutex container_mutex;
 
+static void lazyinit_ignorevec()
+{
+	if (ignorevec_initialized)
+		return;
+
+	opts.ignore = getenv("HEAPTRACE_IGNORE");
+	if (opts.ignore) {
+		std::ifstream file(opts.ignore);
+		if (file.is_open()) {
+			std::string line;
+			while (std::getline(file, line)) {
+				ignorevec.push_back(line);
+			}
+			file.close();
+		}
+		else {
+			pr_out("Failed to open file %s\n", opts.ignore);
+		}
+	}
+	ignorevec_initialized = true;
+}
+
+static bool is_ignored(const std::string &report)
+{
+	lazyinit_ignorevec();
+	return std::any_of(ignorevec.begin(), ignorevec.end(), [&report](const std::string& s)
+			   { return report.find(s) != std::string::npos; });
+}
+
 // record_backtrace() is defined in stacktrace.h as an inline function.
 void __record_backtrace(size_t size, void *addr, stack_trace_t &stack_trace, int nptrs)
 {