fix compile on Linux

CMakeLists.txt

@@ -20,18 +20,18 @@ if (${ARCH} STREQUAL i386)
     if(APPLE)
         set(PREFIX          i386-elf-)
     endif ()
-    set(CMAKE_C_FLAGS       "-fno-builtin -Wall -ggdb -nostdinc -m32")
+    set(CMAKE_C_FLAGS       "-m32")
 elseif (${ARCH} STREQUAL x86_64)
     if(APPLE)
         set(PREFIX          x86_64-elf-)
     endif ()
-    set(CMAKE_C_FLAGS       "-fno-builtin -Wall -ggdb -nostdinc -m64")
+    set(CMAKE_C_FLAGS       "-m64")
 elseif (${ARCH} STREQUAL riscv32)
     set(PREFIX              riscv64-unknown-elf-)
-    set(CMAKE_C_FLAGS       "-march=rv32imac -mabi=ilp32 -mcmodel=medany -std=gnu99 -fno-builtin -Wall -nostdinc -fno-stack-protector -ffunction-sections -fdata-sections")
+    set(CMAKE_C_FLAGS       "-march=rv32imac -mabi=ilp32 -mcmodel=medany")
 elseif (${ARCH} STREQUAL riscv64)
     set(PREFIX              riscv64-unknown-elf-)
-    set(CMAKE_C_FLAGS       "-march=rv64imac -mabi=lp64 -mcmodel=medany -std=gnu99 -fno-builtin -Wall -nostdinc -fno-stack-protector -ffunction-sections -fdata-sections")
+    set(CMAKE_C_FLAGS       "-march=rv64imac -mabi=lp64 -mcmodel=medany")
 elseif (${ARCH} STREQUAL aarch64)
     set(PREFIX              aarch64-none-elf-)
 else()
@@ -39,7 +39,9 @@ else()
 endif ()
 set(CMAKE_C_COMPILER        ${PREFIX}gcc)
 set(CMAKE_RANLIB            ${PREFIX}ranlib)
+set(CMAKE_C_FLAGS           "${CMAKE_C_FLAGS} -fno-builtin -nostdinc -fno-stack-protector -ggdb -Wall")
 set(CMAKE_EXE_LINKER_FLAGS  "-nostdlib")
+set(CMAKE_SHARED_LIBRARY_LINK_C_FLAGS) # get rid of '-rdynamic' on Linux
 
 # Library
 add_library(ulib ${LIBS})