[libc++] Increase the constexpr steps limit on some bitset tests.

Prevent these tests from failing on some platforms (the number of
constexpr steps increased by https://reviews.llvm.org/D154860).

Author: var-const

libcxx/test/std/utilities/template.bitset/bitset.members/op_or_eq.pass.cpp

@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// ADDITIONAL_COMPILE_FLAGS(has-fconstexpr-steps): -fconstexpr-steps=15000000
+
 // bitset<N>& operator|=(const bitset<N>& rhs); // constexpr since C++23
 
 #include <bitset>

libcxx/test/std/utilities/template.bitset/bitset.members/right_shift_eq.pass.cpp

@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// ADDITIONAL_COMPILE_FLAGS(has-fconstexpr-steps): -fconstexpr-steps=15000000
+
 // bitset<N>& operator<<=(size_t pos); // constexpr since C++23
 
 #include <bitset>