Introduce an -fpeel-loops flag for GCC build.

This improves performance of scalar-optimized code by 1.5 times as well as fixes gost-engine#433.

CMakeLists.txt

@@ -26,14 +26,14 @@ include_directories(${OPENSSL_INCLUDE_DIR})
 set(OPENSSL_MODULES_DIR ${CMAKE_INSTALL_LIBDIR}/ossl-modules)
 
 if (CMAKE_C_COMPILER_ID MATCHES "Clang")
-  set(CMAKE_C_FLAGS_RELEASE -O2)
+  set(CMAKE_C_FLAGS_RELEASE "-O2")
   set(CMAKE_C_FLAGS_DEBUG "-O0 -ggdb")
   set(CMAKE_C_FLAGS_RELWITHDEBINFO "-O2 -ggdb")
   add_compile_options(-Werror -Wall -Wno-unused-parameter -Wno-unused-function -Wno-missing-braces -Qunused-arguments -Wno-deprecated-declarations)
 elseif(CMAKE_C_COMPILER_ID MATCHES "GNU")
-  set(CMAKE_C_FLAGS_RELEASE -O2)
+  set(CMAKE_C_FLAGS_RELEASE "-O2 -fpeel-loops")
   set(CMAKE_C_FLAGS_DEBUG "-O0 -ggdb")
-  set(CMAKE_C_FLAGS_RELWITHDEBINFO "-O2 -ggdb")
+  set(CMAKE_C_FLAGS_RELWITHDEBINFO "-O2 -fpeel-loops -ggdb")
   add_compile_options(-Werror -Wall -Wno-unused-parameter -Wno-unused-function -Wno-missing-braces -Wno-error=unknown-pragmas -Wno-error=pragmas -Wno-deprecated-declarations)
 elseif(CMAKE_C_COMPILER_ID MATCHES "MSVC")
   add_definitions(-D_CRT_SECURE_NO_WARNINGS)