Merge bitcoin/bitcoin#28479: build: use _LIBCPP_ENABLE_DEBUG_MODE over ENABLE_ASSERTIONS

4a82503 build: use _LIBCPP_ENABLE_DEBUG_MODE over ENABLE_ASSERTIONS (fanquake)

Pull request description:

  `_LIBCPP_ENABLE_ASSERTIONS` is deprecated, and will be removed. [See (from libc++ __config in main)](https://github.com/llvm/llvm-project/blob/b57df9fe9a1a230f277d671bfa0884bbda9fc1c5/libcxx/include/__config#L205-L209):

  > TODO(hardening): remove this in LLVM 19.
  > This is for backward compatibility -- make enabling `_LIBCPP_ENABLE_ASSERTIONS` (which predates hardening modes)
  > equivalent to setting the safe mode.
  > ifdef _LIBCPP_ENABLE_ASSERTIONS
  > warning "_LIBCPP_ENABLE_ASSERTIONS is deprecated, please use _LIBCPP_ENABLE_SAFE_MODE instead."

  From LLVM 17, `_LIBCPP_ENABLE_DEBUG_MODE` can be used instead, which also performs more checks than safe mode:

  > Enables the debug mode which contains all the checks from the hardened mode and additionally more expensive checks that may affect the complexity of algorithms. The debug mode is intended to be used for testing, not in production. Mutually exclusive with `_LIBCPP_ENABLE_HARDENED_MODE` and `_LIBCPP_ENABLE_SAFE_MODE`.

  See https://libcxx.llvm.org/Hardening.html.

  Related to #28476.

ACKs for top commit:
  MarcoFalke:
    lgtm ACK 4a82503 🙏

Tree-SHA512: ca52603f86214e8e9350bd2b2baa44fbde0f72f1b186da7aecd8690256dff5b2be75fe89383158298a6f683bbd6ae0dff528d2ba4cc5ece1f56cfbdee0e1dc5d

Author: fanquake

depends/hosts/linux.mk

@@ -17,7 +17,7 @@ linux_release_CXXFLAGS=$(linux_release_CFLAGS)
 linux_debug_CFLAGS=-O1
 linux_debug_CXXFLAGS=$(linux_debug_CFLAGS)
 
-linux_debug_CPPFLAGS=-D_GLIBCXX_DEBUG -D_GLIBCXX_DEBUG_PEDANTIC -D_LIBCPP_ENABLE_ASSERTIONS=1
+linux_debug_CPPFLAGS=-D_GLIBCXX_DEBUG -D_GLIBCXX_DEBUG_PEDANTIC -D_LIBCPP_ENABLE_DEBUG_MODE=1
 
 ifeq (86,$(findstring 86,$(build_arch)))
 i686_linux_CC=gcc -m32