Don't overwrite all of CFLAGS/CXXFLAGS in prometheus-cpp build

We only really care about the -DDEBUG flag. We need to pass other flags
down from various builds such as the binary builds on OBS.

FindPrometheusCpp.cmake

@@ -6,13 +6,14 @@ set(prometheuscpp_src "${CMAKE_CURRENT_SOURCE_DIR}/auxil/prometheus-cpp")
 set(_sharedlibs ${BUILD_SHARED_LIBS})
 set(BUILD_SHARED_LIBS OFF)
 
-# These need to be reset before setting up Prometheus because otherwise it picks up
-# the -DDEBUG from SetDefaultCompileFlags and causes civetweb to output a bunch of
-# debugging information. Let the library figure out its own flags.
+# The -DDEBUG flag from SetDefaultCompileFlags causes civetweb in prometheus-cpp
+# to output a bunch of debugging information. Remove it from the flags before
+# allowing them to pass through to the prometheus-cpp build.
 set(_cxxflags ${CMAKE_CXX_FLAGS})
-set(CMAKE_CXX_FLAGS "")
 set(_cflags ${CMAKE_C_FLAGS})
-set(CMAKE_C_FLAGS "")
+
+string(REPLACE "-DDEBUG" "" CMAKE_CXX_FLAGS "${_cxxflags}")
+string(REPLACE "-DDEBUG" "" CMAKE_C_FLAGS "${_cflags}")
 
 option(ENABLE_PUSH "" OFF)
 option(ENABLE_TESTING "" OFF)
@@ -25,7 +26,6 @@ message("=======================================================================
 
 set(zeekdeps ${zeekdeps} prometheus-cpp::core prometheus-cpp::pull)
 include_directories(BEFORE ${prometheuscpp_src}/pull/include ${prometheuscpp_src}/core/include)
-#include_directories(BEFORE ${prometheuscpp_src}/3rdparty/civetweb/include)
 include_directories(BEFORE ${prometheuscpp_build}/pull/include ${prometheuscpp_build}/core/include)
 
 set(BUILD_SHARED_LIBS ${_sharedlibs})