Build fail if CMake with CURL_WERROR

[concatime]

I tried to build curl with CMake using CURL_WERROR flag. The issue is that I’m getting this error:

 # cmake .. -GNinja -DCMAKE_USE_MBEDTLS=1 -DCMAKE_USE_OPENSSL=0 -DCURL_ZLIB=1 -DCURL_WERROR=1 -DUSE_NGHTTP2=1 -DENABLE_ARES=1
 […]
 # ninja
[4/763] Building C object lib/CMakeFiles/libcurl.dir/cookie.c.o
FAILED: lib/CMakeFiles/libcurl.dir/cookie.c.o 
 […]
lib/CMakeFiles/libcurl.dir/cookie.c.o   -c ../lib/cookie.c
In file included from ../lib/curl_setup.h:56:0,
                 from ../lib/cookie.c:83:
lib/curl_config.h:987:19: error: two or more data types in declaration specifiers
 #define in_addr_t unsigned long
                   ^
lib/curl_config.h:987:28: error: two or more data types in declaration specifiers
 #define in_addr_t unsigned long
                            ^
[5/763] Building C object lib/CMakeFiles/libcurl.dir/http.c.o
FAILED: lib/CMakeFiles/libcurl.dir/http.c.o 
 […]
lib/CMakeFiles/libcurl.dir/http.c.o   -c ../lib/http.c
In file included from ../lib/curl_setup.h:56:0,
                 from ../lib/http.c:23:
lib/curl_config.h:987:19: error: two or more data types in declaration specifiers
 #define in_addr_t unsigned long
                   ^
lib/curl_config.h:987:28: error: two or more data types in declaration specifiers
 #define in_addr_t unsigned long
                            ^
ninja: build stopped: subcommand failed.

The line #define in_addr_t unsigned long should be present only once according to this comment.

[snikulov]

@bagder @concatime Confirmed.

The problem is - when we enforce treat warnings as errors rule, then some symbols checks are failed because of warnings.
For example check for HAVE_IN_ADDR_T failed and we have redefinition in curl_config.h

1. a short fix, we can move CMAKE_C_FLAGS altering with -Werror below all checks.
2. long fix - dig into configuration checks and investigate and fix all possible warnings

Will try to fix it shortly.