Add a few missing features to the cmake setup that are present in configure.ac:

Include all compiler warnings, and provide DISABLE_WERROR to make them not be errors.
 Define _REENTRANT, if setting it works.
 Set -Bsymbolic-functions, and provide DISABLE_BSYMBOLIC to turn that off.
 Implement the check for HAS_GNU_WARNING_LONG

CMakeLists.txt

@@ -48,7 +48,8 @@ option(BUILD_SHARED_LIBS  "Default to building shared libraries" ON)
 # Enable or disable features. By default, all features are turned off.
 option(ENABLE_RDRAND                "Enable RDRAND Hardware RNG Hash Seed"          OFF)
 option(ENABLE_THREADING             "Enable partial threading support."             OFF)
-option(HAS_GNU_WARNING_LONG         "Define if .gnu.warning accepts long strings."  OFF)
+option(DISABLE_WERROR               "Avoid treating compiler warnings as fatal errors"    OFF)
+option(DISABLE_BSYMBOLIC            "Avoid linking with -Bsymbolic-function"   OFF)
 
 if (UNIX OR MINGW OR CYGWIN)
     list(APPEND CMAKE_REQUIRED_DEFINITIONS -D_GNU_SOURCE)
@@ -70,6 +71,7 @@ check_include_file(strings.h        HAVE_STRINGS_H)
 check_include_file(string.h         HAVE_STRING_H)
 check_include_file(syslog.h         HAVE_SYSLOG_H)
 
+
 check_include_files("stdlib.h;stdarg.h;string.h;float.h" STDC_HEADERS)
 
 check_include_file(unistd.h         HAVE_UNISTD_H)
@@ -147,12 +149,21 @@ if (MSVC)
     endif()
 endif()
 
+
 check_type_size(int                 SIZEOF_INT)
 check_type_size(int64_t             SIZEOF_INT64_T)
 check_type_size(long                SIZEOF_LONG)
 check_type_size("long long"         SIZEOF_LONG_LONG)
 check_type_size("size_t"            SIZEOF_SIZE_T)
 
+check_c_source_compiles(
+[=[
+extern void json_object_get();
+__asm__(".section .gnu.json_object_get\\n\\t.ascii \\"Please link against libjson-c instead of libjson\\"\\n\\t.text");
+int main(int c, char *v) { return 0;}
+]=]
+HAS_GNU_WARNING_LONG)
+
 check_c_source_compiles(
   "int main() { int i, x = 0; i = __sync_add_and_fetch(&x,1); return x; }"
   HAVE_ATOMIC_BUILTINS)
@@ -180,8 +191,15 @@ message(STATUS "Written ${PROJECT_BINARY_DIR}/json_config.h")
 
 if ("${CMAKE_C_COMPILER_ID}" STREQUAL "GNU")
     set(CMAKE_C_FLAGS           "${CMAKE_C_FLAGS} -ffunction-sections -fdata-sections")
-    # There's a catch here.
-    set(CMAKE_C_FLAGS           "${CMAKE_C_FLAGS} -Werror")
+	if ("${DISABLE_WERROR}" STREQUAL "OFF")
+	    set(CMAKE_C_FLAGS           "${CMAKE_C_FLAGS} -Werror")
+	endif()
+    set(CMAKE_C_FLAGS           "${CMAKE_C_FLAGS} -Wall")
+    set(CMAKE_C_FLAGS           "${CMAKE_C_FLAGS} -Wcast-qual")
+    set(CMAKE_C_FLAGS           "${CMAKE_C_FLAGS} -Wno-error=deprecated-declarations")
+    set(CMAKE_C_FLAGS           "${CMAKE_C_FLAGS} -Wextra")
+    set(CMAKE_C_FLAGS           "${CMAKE_C_FLAGS} -Wwrite-strings")
+    set(CMAKE_C_FLAGS           "${CMAKE_C_FLAGS} -Wno-unused-parameter")
 
     add_definitions(-D_GNU_SOURCE)
 elseif ("${CMAKE_C_COMPILER_ID}" STREQUAL "MSVC")
@@ -195,6 +213,30 @@ elseif ("${CMAKE_C_COMPILER_ID}" STREQUAL "MSVC")
     set(CMAKE_C_FLAGS           "${CMAKE_C_FLAGS} /wd4701")
 endif()
 
+if (NOT ("${CMAKE_C_COMPILER_ID}" STREQUAL "MSVC"))
+	check_c_source_compiles(
+	[=[
+	/* uClibc toolchains without threading barf when _REENTRANT is defined */
+	#define _REENTRANT 1
+	#include <sys/types.h>
+	int main ()
+	{
+	  return 0;
+	}
+	]=]
+	REENTRANT_WORKS
+	)
+	if (REENTRANT_WORKS)
+		add_compile_options("-D_REENTRANT")
+	endif()
+
+	if (DISABLE_BSYMBOLIC STREQUAL "OFF")
+		set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKED_FLAGS} -Wl,-Bsymbolic-functions")
+		# XXX need cmake>=3.13 for this:
+		#add_link_options("-Wl,-Bsymbolic-functions")
+	endif()
+endif()
+
 if ($ENV{VALGRIND})
 	# Build so that valgrind doesn't complain about linkhash.c
     add_definitions(-DVALGRIND=1)