Fix compilation issue for local installation

[vikman90]

Related issue
#3336

Description

The TARGET=local definition conflicts with a parameter in the libffi's Makefile. That makes libffi compile the sources into src/external/libffi/server. However, in local mode, it tries to compile into src/external/libffi/local, this prevents the Wazuh's Makefile from finding the library while assembling libwazuhext.so.

Solution

The most simple fix is let the Wazuh's Makefile find libffi.a in a location that depends on the TARGET variable.

If we undefined TARGET, we would need to find the default target directory for libffi, that depends on the architecture.

Output

make TARGET=local

General settings:
    TARGET:             local
    V:
    DEBUG:              yes
    DEBUGAD
    PREFIX:             /var/ossec
    MAXAGENTS:          14000
    DATABASE:
    ONEWAY:             no
    CLEANFULL:          no
    RESOURCES_URL:      https://packages.wazuh.com/deps/3.9
User settings:
    OSSEC_GROUP:        ossec
    OSSEC_USER:         ossec
    OSSEC_USER_MAIL:    ossecm
    OSSEC_USER_REM:     ossecr
USE settings:
    USE_ZEROMQ:         no
    USE_GEOIP:          no
    USE_PRELUDE:        no
    USE_INOTIFY:        no
    USE_BIG_ENDIAN:     no
    USE_SELINUX:        no
    USE_AUDIT:          yes
    USE_FRAMEWORK_LIB:  no
Mysql settings:
    includes:
    libs:
Pgsql settings:
    includes:
    libs:
Defines:
    -DMAX_AGENTS=14000 -DOSSECHIDS -DDEFAULTDIR="/var/ossec" -DUSER="ossec" -DREMUSER="ossecr" -DGROUPGLOBAL="ossec" -DMAILUSER="ossecm" -DLinux -DINOTIFY_ENABLED -D_XOPEN_SOURCE=600 -D_GNU_SOURCE -DENABLE_SYSC -DENABLE_CISCAT -DENABLE_SHARED -DENABLE_AUDIT -DLOCAL
Compiler:
    CFLAGS            -Wl,--start-group -Iexternal/audit-userspace/lib -pthread -Iexternal/libdb/build_unix/ -g  -DMAX_AGENTS=14000 -DOSSECHIDS -DDEFAULTDIR="/var/ossec" -DUSER="ossec" -DREMUSER="ossecr" -DGROUPGLOBAL="ossec" -DMAILUSER="ossecm" -DLinux -DINOTIFY_ENABLED -D_XOPEN_SOURCE=600 -D_GNU_SOURCE -DENABLE_SYSC -DENABLE_CISCAT -DENABLE_SHARED -DENABLE_AUDIT -DLOCAL -pipe -Wall -Wextra -I./ -I./headers/ -Iexternal/openssl/include -Iexternal/cJSON/ -Iexternal/libyaml/include -Iexternal/curl/include -Iexternal/msgpack/include
    LDFLAGS            '-Wl,-rpath,/../lib' -pthread -lrt -ldl
    CC                cc
    MAKE              make
make[1]: Leaving directory `/root/wazuh/src'

Done building local

• Compilation without warnings in every supported platform.
  • Linux (local installation)
  • MAC OS X (local installation). The compilation fails (The manager won't compile Python on macOS #3338).
• Source installation.
• Package installation. It applies neither to manager nor agents.