[clang-tidy][NFC] Fix modernize-deprecated-headers findings

Fix issues found by clang-tidy in clang-tidy source directory.
diff --git a/clang-tools-extra/clang-tidy/altera/StructPackAlignCheck.cpp b/clang-tools-extra/clang-tidy/altera/StructPackAlignCheck.cpp
index 70a6ab3..ac458d4 100644
--- a/clang-tools-extra/clang-tidy/altera/StructPackAlignCheck.cpp
+++ b/clang-tools-extra/clang-tidy/altera/StructPackAlignCheck.cpp
@@ -10,7 +10,7 @@
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/RecordLayout.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
-#include <math.h>
+#include <cmath>
 
 using namespace clang::ast_matchers;