Import lwIP contrib rep

... from http://git.savannah.gnu.org/cgit/lwip/lwip-contrib.git/ into contrib/ subdir, STABLE-2_1_0_RELEASE tag
lwIP contrib is now officially frozen
TODO: Fix build

contrib/ports/CMakeCommon.cmake

@@ -0,0 +1,105 @@
+# ARM mbedtls support https://tls.mbed.org/
+set(MBEDTLSDIR ${LWIP_CONTRIB_DIR}/../mbedtls)
+if(EXISTS ${MBEDTLSDIR}/CMakeLists.txt)
+    set(LWIP_HAVE_MBEDTLS ON BOOL)
+
+    # Prevent building MBEDTLS programs and tests
+    set(ENABLE_PROGRAMS OFF CACHE BOOL "")
+    set(ENABLE_TESTING  OFF CACHE BOOL "")
+    
+    # mbedtls uses cmake. Sweet!
+    add_subdirectory(${MBEDTLSDIR} mbedtls)
+
+    set (LWIP_MBEDTLS_DEFINITIONS
+        -DLWIP_HAVE_MBEDTLS=1
+    )
+    set (LWIP_MBEDTLS_INCLUDE_DIRS
+        ${MBEDTLSDIR}/include
+    )
+    set (LWIP_MBEDTLS_LINK_LIBRARIES
+        mbedtls
+        mbedcrypto
+        mbedx509
+    )
+endif()
+
+set(LWIP_COMPILER_FLAGS_GNU_CLANG
+    -g
+    -Wall
+    -pedantic
+    -Werror
+    -Wparentheses
+    -Wsequence-point
+    -Wswitch-default
+    -Wextra -Wundef
+    -Wshadow
+    -Wpointer-arith
+    -Wcast-qual
+    -Wc++-compat
+    -Wwrite-strings
+    -Wold-style-definition
+    -Wcast-align
+    -Wmissing-prototypes
+    -Wnested-externs
+    -Wunreachable-code
+    -Wuninitialized
+    -Wmissing-prototypes
+    -Waggregate-return
+    -Wlogical-not-parentheses
+)
+
+if (NOT LWIP_HAVE_MBEDTLS)
+    list(APPEND LWIP_COMPILER_FLAGS_GNU_CLANG
+        -Wredundant-decls
+    )
+endif()
+
+if(CMAKE_C_COMPILER_ID STREQUAL GNU)
+    list(APPEND LWIP_COMPILER_FLAGS_GNU_CLANG
+        -Wlogical-op
+        -Wtrampolines
+    )
+
+    if (NOT LWIP_HAVE_MBEDTLS)
+        list(APPEND LWIP_COMPILER_FLAGS_GNU_CLANG
+            -Wc90-c99-compat
+        )
+    endif()
+
+    if(NOT CMAKE_C_COMPILER_VERSION VERSION_LESS 4.9)
+        if(LWIP_USE_SANITIZERS)
+            list(APPEND LWIP_COMPILER_FLAGS_GNU_CLANG
+                -fsanitize=address
+                -fsanitize=undefined
+                -fno-sanitize=alignment
+                -fstack-protector
+                -fstack-check
+            )
+            set(LWIP_SANITIZER_LIBS asan ubsan)
+        endif()
+    endif()
+
+    set(LWIP_COMPILER_FLAGS ${LWIP_COMPILER_FLAGS_GNU_CLANG})
+endif()
+
+if(CMAKE_C_COMPILER_ID STREQUAL Clang)
+    list(APPEND LWIP_COMPILER_FLAGS_GNU_CLANG
+        -Wdocumentation
+        -Wno-documentation-deprecated-sync
+    )
+
+    if(LWIP_USE_SANITIZERS)
+        list(APPEND LWIP_COMPILER_FLAGS_GNU_CLANG
+            -fsanitize=address
+            -fsanitize=undefined
+            -fno-sanitize=alignment
+        )
+        set(LWIP_SANITIZER_LIBS asan ubsan)
+    endif()
+
+    set(LWIP_COMPILER_FLAGS ${LWIP_COMPILER_FLAGS_GNU_CLANG})
+endif()
+
+if(CMAKE_C_COMPILER_ID STREQUAL MSVC)
+    # TODO
+endif()