build: support of build without C++ compiler

Signed-off-by: Marat Abrarov <abrarov@gmail.com>

Author: mabrarov

CMakeLists.txt

@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.12)
-project(fluent-bit LANGUAGES C CXX)
+project(fluent-bit C)
 
 # CMP0069 ensures that LTO is enabled for all compilers
 cmake_policy(SET CMP0069 NEW)
@@ -54,6 +54,9 @@ if(CMAKE_SYSTEM_NAME MATCHES "Linux")
   endif()
 endif()
 
+set(FLB_EXTRA_CMAKE_CXX_FLAGS)
+set(FLB_EXTRA_CMAKE_CXX_LINK_FLAGS)
+
 # Update CFLAGS
 if (MSVC)
   # Use static C/C++ runtime
@@ -66,8 +69,6 @@ if (MSVC)
     string(TOUPPER ${config_type} upper_config_type)
     set(flag_var "CMAKE_C_FLAGS_${upper_config_type}")
     string(REGEX REPLACE "(^| |\\t|\\r|\\n)(-|/)(MD)(d?)($| |\\t|\\r|\\n)" "\\1\\2MT\\4\\5" ${flag_var} "${${flag_var}}")
-    set(flag_var "CMAKE_CXX_FLAGS_${upper_config_type}")
-    string(REGEX REPLACE "(^| |\\t|\\r|\\n)(-|/)(MD)(d?)($| |\\t|\\r|\\n)" "\\1\\2MT\\4\\5" ${flag_var} "${${flag_var}}")
   endforeach()
   set(flag_var)
   set(upper_config_type)
@@ -117,17 +118,26 @@ else()
 endif()
 
 set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -D__FLB_FILENAME__=__FILE__")
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -D__FLB_FILENAME__=__FILE__")
+# CMAKE_CXX_FLAGS will extended with FLB_EXTRA_CMAKE_CXX_FLAGS,
+# when / if C++ language support is enabled.
+# Until C++ language support is enabled, CMAKE_CXX_FLAGS is empty / undefined.
+set(FLB_EXTRA_CMAKE_CXX_FLAGS "${FLB_EXTRA_CMAKE_CXX_FLAGS} -D__FLB_FILENAME__=__FILE__")
 
 if(${CMAKE_SYSTEM_PROCESSOR} MATCHES "armv7l")
   set(CMAKE_C_LINK_FLAGS "${CMAKE_C_LINK_FLAGS} -latomic")
-  set(CMAKE_CXX_LINK_FLAGS "${CMAKE_CXX_LINK_FLAGS} -latomic")
+  # CMAKE_CXX_LINK_FLAGS will extended with FLB_EXTRA_CMAKE_CXX_LINK_FLAGS,
+  # when / if C++ language support is enabled.
+  # Until C++ language support is enabled, CMAKE_CXX_LINK_FLAGS is empty / undefined.
+  set(FLB_EXTRA_CMAKE_CXX_LINK_FLAGS "${FLB_EXTRA_CMAKE_CXX_LINK_FLAGS} -latomic")
 endif()
 if(${CMAKE_SYSTEM_NAME} MATCHES "FreeBSD")
   set(FLB_SYSTEM_FREEBSD On)
   add_definitions(-DFLB_SYSTEM_FREEBSD)
   set(CMAKE_C_LINK_FLAGS "${CMAKE_C_LINK_FLAGS} -lutil")
-  set(CMAKE_CXX_LINK_FLAGS "${CMAKE_CXX_LINK_FLAGS} -lutil")
+  # CMAKE_CXX_LINK_FLAGS will extended with FLB_EXTRA_CMAKE_CXX_LINK_FLAGS,
+  # when / if C++ language support is enabled.
+  # Until C++ language support is enabled, CMAKE_CXX_LINK_FLAGS is empty / undefined.
+  set(FLB_EXTRA_CMAKE_CXX_LINK_FLAGS "${FLB_EXTRA_CMAKE_CXX_LINK_FLAGS} -lutil")
 endif()
 
 # *BSD is not supported platform for wasm-micro-runtime except for FreeBSD.
@@ -469,7 +479,10 @@ endif()
 if(FLB_COVERAGE)
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -g -O0 --coverage -fprofile-arcs -ftest-coverage")
   if (FLB_UNICODE_ENCODER)
-    set(CMAKE_CXX_FLAGS "${CMAKE_C_FLAGS} -g -O0 --coverage -fprofile-arcs -ftest-coverage")
+    # CMAKE_CXX_FLAGS will extended with FLB_EXTRA_CMAKE_CXX_FLAGS,
+    # when / if C++ language support is enabled.
+    # Until C++ language support is enabled, CMAKE_CXX_FLAGS is empty / undefined.
+    set(FLB_EXTRA_CMAKE_CXX_FLAGS "${FLB_EXTRA_CMAKE_CXX_FLAGS} -g -O0 --coverage -fprofile-arcs -ftest-coverage")
   endif()
   set(CMAKE_BUILD_TYPE "Debug")
 endif()
@@ -690,6 +703,22 @@ if(FLB_UNICODE_ENCODER AND FLB_USE_SIMDUTF)
     message(FATAL_ERROR "FLB_UNICODE_ENCODER requires FLB_USE_SIMDUTF")
   endif()
   enable_language(CXX)
+
+  # Perform delayed modification / extension of CMAKE_CXX_* variables.
+  if (MSVC)
+    # Replace (/|-)MD(d?) with (/|-)MT(d?) to avoid D9025 warning
+    foreach(config_type ${CMAKE_CONFIGURATION_TYPES} ${CMAKE_BUILD_TYPE} Debug Release RelWithDebInfo MinSizeRel)
+      string(TOUPPER ${config_type} upper_config_type)
+      set(flag_var "CMAKE_CXX_FLAGS_${upper_config_type}")
+      string(REGEX REPLACE "(^| |\\t|\\r|\\n)(-|/)(MD)(d?)($| |\\t|\\r|\\n)" "\\1\\2MT\\4\\5" ${flag_var} "${${flag_var}}")
+    endforeach()
+    set(flag_var)
+    set(upper_config_type)
+    set(config_type)
+  endif()
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${FLB_EXTRA_CMAKE_CXX_FLAGS}")
+  set(CMAKE_CXX_LINK_FLAGS "${CMAKE_CXX_LINK_FLAGS} ${FLB_EXTRA_CMAKE_CXX_LINK_FLAGS}")
+
   set (CMAKE_CXX_STANDARD 11)
   add_subdirectory(${FLB_PATH_LIB_SIMDUTF} EXCLUDE_FROM_ALL)
   FLB_DEFINITION(FLB_HAVE_UNICODE_ENCODER)

lib/onigmo/CMakeLists.txt

@@ -40,8 +40,6 @@ if (MSVC)
     string(TOUPPER ${config_type} upper_config_type)
     set(flag_var "CMAKE_C_FLAGS_${upper_config_type}")
     string(REGEX REPLACE "(^| |\\t|\\r|\\n)(-|/)(MD)(d?)($| |\\t|\\r|\\n)" "\\1\\2MT\\4\\5" ${flag_var} "${${flag_var}}")
-    set(flag_var "CMAKE_CXX_FLAGS_${upper_config_type}")
-    string(REGEX REPLACE "(^| |\\t|\\r|\\n)(-|/)(MD)(d?)($| |\\t|\\r|\\n)" "\\1\\2MT\\4\\5" ${flag_var} "${${flag_var}}")
   endforeach()
   set(flag_var)
   set(upper_config_type)