CMake: detect required header for STACKTRACE feature

musl does not provide execinfo.h, so our current stacktrace-related
code cannot be used with it.

CMakeLists.txt

@@ -19,6 +19,7 @@ set(minLibtorrentVersion 1.2.11)
 set(minZlibVersion 1.2.11)
 
 # features (some are platform-specific)
+include(CheckCXXSourceCompiles) # TODO: migrate to CheckSourceCompiles in CMake >= 3.19
 include(FeatureSummary)
 include(FeatureOptionsSetup)
 feature_option(STACKTRACE "Enable stacktraces" ON)
@@ -34,6 +35,18 @@ if (CMAKE_SYSTEM_NAME STREQUAL "Linux")
         "Install systemd service file to a directory manually overridable with Systemd_SERVICES_INSTALL_DIR"
         OFF "NOT GUI" OFF
     )
+    if (STACKTRACE)
+        check_cxx_source_compiles(
+            "#include <execinfo.h>
+            int main(){return 0;}"
+            QBITTORRENT_HAS_EXECINFO_H
+        )
+        if (NOT QBITTORRENT_HAS_EXECINFO_H)
+            message(FATAL_ERROR "execinfo.h header file not found.\n"
+                "Please either disable the STACKTRACE feature or use a libc that has this header file, such as glibc (GNU libc)."
+            )
+        endif()
+    endif()
 elseif (MSVC)
     feature_option(MSVC_RUNTIME_DYNAMIC "Use MSVC dynamic runtime library (-MD) instead of static (-MT)" ON)
 endif()