--- gmic-3.5.2.old/src/Makefile
+++ gmic-3.5.2/src/Makefile
@@ -216,8 +216,8 @@
 OPT_LIBS = # ${FLTO}
 endif
 ifdef IS_CLANG
-OPT_CFLAGS = -O3 -mtune=generic --stdlib=libc++ # '-Ofast' makes things unstable
-OPT_LIBS = ${FLTO}
+OPT_CFLAGS = -O3 -mtune=generic # '-Ofast' makes things unstable
+OPT_LIBS =
 endif
 ifdef icpc
 OPT_CFLAGS = -fast
--- gmic-3.5.2.old/src/Makefile
+++ gmic-3.5.2/src/Makefile
@@ -233,8 +233,8 @@
 # Enable parallelization, using OpenMP.
 # (http://www.openmp.org/)
 ifdef IS_CLANG
-OPENMP_CFLAGS = -I/usr/lib/gcc/x86_64-linux-gnu/9/include -Dcimg_use_openmp -fopenmp=libomp
-OPENMP_LIBS = -lomp
+OPENMP_CFLAGS =
+OPENMP_LIBS =
 else
 OPENMP_CFLAGS = -fopenmp -Dcimg_use_openmp
 OPENMP_LIBS = -lgomp
--- gmic-3.5.2.old/gmic-qt/CMakeLists.txt
+++ gmic-3.5.2/gmic-qt/CMakeLists.txt
@@ -267,21 +267,6 @@
     TYPE OPTIONAL
     PURPOSE "Optionally used by gmic-qt")
 
-if (OpenMP_FOUND)
-    message(STATUS "G'Mic: using OpenMP ${OpenMP_CXX_VERSION}")
-    link_libraries(OpenMP::OpenMP_CXX)
-    add_definitions(-Dcimg_use_openmp)
-endif()
-
-#
-# LTO option
-#
-
-if (ENABLE_LTO)
-    message(STATUS "Link Time Optimizer enabled")
-    set(CMAKE_INTERPROCEDURAL_OPTIMIZATION TRUE)
-endif()
-
 #
 # Enable CFG
 #