Merge bitcoin/bitcoin#31379: cmake: Fix passing APPEND_*FLAGS to secp256k1 subtree

c4c5cf1 cmake: Fix passing `APPEND_*FLAGS` to `secp256k1` subtree (Hennadii Stepanov)
eb540a2 cmake: Remove `core_sanitizer_{cxx,linker}_flags` helper variables (Hennadii Stepanov)

Pull request description:

  On the master branch @ 70e20ea, the `APPEND_CPPFLAGS`, `APPEND_CFLAGS`  and `APPEND_LDFLAGS` are not correctly applied when building C code in the  `secp256k1` subtree, as intended.

  This behaviour occurs due to two issues:
  1. The command here: https://github.com/bitcoin/bitcoin/blob/70e20ea024ce4f39abc4022e1ba19d5a6db2a207/src/CMakeLists.txt#L77
  does not affect the code in `add_subdirectory(secp256k1)` above it.

  2.  `APPEND_LDFLAGS`  is not passed to the subtree's build system at all.

  This PR fixes both issues.

  Additionally, the helper variables `core_sanitizer_cxx_flags` and `core_sanitizer_linker_flags` have been removed.

ACKs for top commit:
  theuni:
    utACK c4c5cf1.
  TheCharlatan:
    ACK c4c5cf1

Tree-SHA512: 707acfa623f0436e34e9e6ba8ce2979e0fde5e196e2242fd1cde4c50f433938549781193d8a06419a0866bbe6d69d76f8383d973afbd87d944407963b318c5c9

Author: fanquake

src/CMakeLists.txt

@@ -50,12 +50,13 @@ set(SECP256K1_BUILD_EXAMPLES OFF CACHE BOOL "" FORCE)
 include(GetTargetInterface)
 # -fsanitize and related flags apply to both C++ and C,
 # so we can pass them down to libsecp256k1 as CFLAGS and LDFLAGS.
-get_target_interface(core_sanitizer_cxx_flags "" sanitize_interface COMPILE_OPTIONS)
-set(SECP256K1_APPEND_CFLAGS ${core_sanitizer_cxx_flags} CACHE STRING "" FORCE)
-unset(core_sanitizer_cxx_flags)
-get_target_interface(core_sanitizer_linker_flags "" sanitize_interface LINK_OPTIONS)
-set(SECP256K1_APPEND_LDFLAGS ${core_sanitizer_linker_flags} CACHE STRING "" FORCE)
-unset(core_sanitizer_linker_flags)
+get_target_interface(SECP256K1_APPEND_CFLAGS "" sanitize_interface COMPILE_OPTIONS)
+string(STRIP "${SECP256K1_APPEND_CFLAGS} ${APPEND_CPPFLAGS}" SECP256K1_APPEND_CFLAGS)
+string(STRIP "${SECP256K1_APPEND_CFLAGS} ${APPEND_CFLAGS}" SECP256K1_APPEND_CFLAGS)
+set(SECP256K1_APPEND_CFLAGS ${SECP256K1_APPEND_CFLAGS} CACHE STRING "" FORCE)
+get_target_interface(SECP256K1_APPEND_LDFLAGS "" sanitize_interface LINK_OPTIONS)
+string(STRIP "${SECP256K1_APPEND_LDFLAGS} ${APPEND_LDFLAGS}" SECP256K1_APPEND_LDFLAGS)
+set(SECP256K1_APPEND_LDFLAGS ${SECP256K1_APPEND_LDFLAGS} CACHE STRING "" FORCE)
 # We want to build libsecp256k1 with the most tested RelWithDebInfo configuration.
 enable_language(C)
 foreach(config IN LISTS CMAKE_BUILD_TYPE CMAKE_CONFIGURATION_TYPES)
@@ -76,7 +77,6 @@ set_target_properties(secp256k1 PROPERTIES
   EXCLUDE_FROM_ALL TRUE
 )
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
-string(APPEND CMAKE_C_COMPILE_OBJECT " ${APPEND_CPPFLAGS} ${APPEND_CFLAGS}")
 
 add_library(bitcoin_consensus STATIC EXCLUDE_FROM_ALL
   arith_uint256.cpp