cmake: Fix passing APPEND_*FLAGS to secp256k1 subtree

Author: hebasto

src/CMakeLists.txt

@@ -52,8 +52,11 @@ 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(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)
@@ -75,7 +78,6 @@ 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