From e9c2e6f1276f14659d2e013bb61e511f6984abec Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E2=9C=88=20Graham=20=E2=9C=88?= <plicease@cpan.org>
Date: Sun, 24 Sep 2017 13:52:49 -0400
Subject: [PATCH] Only add warning and std flags if supported by compiler
 (#144)

This fixes errors like those reported in #143 on Solaris
(and probably other platforms where gcc is not the native
compiler):

c99: -W option with unknown program all

This only fixes it for cmake, but presumably similar checks
could be added for autoconf as well.
---
 CMakeLists.txt | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b9a9bd0..a9d5206 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -61,7 +61,27 @@ IF (WIN32)
   # Ignore warning C4996: 'strncpy'
   ADD_DEFINITIONS("-D_CRT_SECURE_NO_WARNINGS=1")
 ELSE()
-  SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Wformat=2 -std=gnu99 -O2 -g")
+  INCLUDE(CheckCCompilerFlag)
+  CHECK_C_COMPILER_FLAG("-Wall" COMPILER_HAS_WALL)
+  IF (COMPILER_HAS_WALL)
+    SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall")
+  ENDIF()
+  CHECK_C_COMPILER_FLAG("-Wextra" COMPILER_HAS_WEXTRA)
+  IF (COMPILER_HAS_WEXTRA)
+    SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wextra")
+  ENDIF()
+  CHECK_C_COMPILER_FLAG("-Wformat=2" COMPILER_HAS_WFORMAT)
+  IF (COMPILER_HAS_WFORMAT)
+    SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wformat=2")
+  ENDIF()
+  CHECK_C_COMPILER_FLAG("-std=gnu99" COMPILER_HAS_STD_GNU99)
+  CHECK_C_COMPILER_FLAG("-std=c99" COMPILER_HAS_STD_C99)
+  IF (COMPILER_HAS_STD_GNU99)
+    SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=gnu99")
+  ELSEIF (COMPILER_HAS_STD_C99)
+    SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -std=c99")
+  ENDIF()
+  SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -O2 -g")
 ENDIF()
 
 INCLUDE_DIRECTORIES(${pkgconf_SOURCE_DIR} ${pkgconf_BINARY_DIR})