cmake: enable choosing CPU extesions

`AUTO_DETECT_ISA` will disable the resolution of the SSE packages
and the user will have to manually set `HAVE_{AVX,AVX2,SSE}`.

Solves #453

Signed-off-by: Filipe Laíns <lains@archlinux.org>

CMakeLists.txt

@@ -67,6 +67,7 @@ option(ENABLE_SRSENB   "Build srsENB application"                 ON)
 option(ENABLE_SRSEPC   "Build srsEPC application"                 ON)
 option(ENABLE_5GNR     "Build with 5G-NR components"              OFF)
 option(DISABLE_SIMD    "disable simd instructions"                OFF)
+option(AUTO_DETECT_ISA "Autodetect supported ISA extensions"      ON)
 
 option(ENABLE_GUI      "Enable GUI (using srsGUI)"                ON)
 option(ENABLE_UHD      "Enable UHD"                               ON)
@@ -329,7 +330,10 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "GNU" OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
   ADD_C_COMPILER_FLAG_IF_AVAILABLE("-Wno-unused-but-set-variable" HAVE_WNO_UNUSED_BUT_SET_VARIABLE)
   ADD_CXX_COMPILER_FLAG_IF_AVAILABLE("-Wno-unused-but-set-variable" HAVE_WNO_UNUSED_BUT_SET_VARIABLE)
 
-  find_package(SSE)
+  if (AUTO_DETECT_ISA)
+    find_package(SSE)
+  endif (AUTO_DETECT_ISA)
+
   if (HAVE_AVX2)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -march=${GCC_ARCH} -mfpmath=sse -mavx2 -DLV_HAVE_AVX2 -DLV_HAVE_AVX -DLV_HAVE_SSE")
   else (HAVE_AVX2)
@@ -380,7 +384,9 @@ if(CMAKE_C_COMPILER_ID MATCHES "GNU" OR CMAKE_C_COMPILER_ID MATCHES "Clang")
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DUSE_GLIBC_IPV6")
   endif (USE_GLIBC_IPV6)
 
-  find_package(SSE)
+  if (AUTO_DETECT_ISA)
+    find_package(SSE)
+  endif (AUTO_DETECT_ISA)
   if (HAVE_AVX2)
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -march=${GCC_ARCH} -mfpmath=sse -mavx2 -DLV_HAVE_AVX2 -DLV_HAVE_AVX -DLV_HAVE_SSE")
   else (HAVE_AVX2)