sounds like you didn't google, since googling this issue shows me that
people tried to include openssl.h. So the issue could be that you are missing openssl-dev. Take a look at pacman's dependencies with:
I initally thought that might be problem and looked at the ./configure output which reported (also libssl-dev is installed) ....... checking whether to link with libssl... yes checking for MD5_Final in -lssl... yes ...... Found library "gpgme" was missing. After installing it below is the following error from signing.c file make[3]: Entering directory `/home/user/tmp/pacman/lib/libalpm' CC signing.lo signing.c: In function 'key_search': signing.c:301:8: error: 'GPGME_PK_ECDSA' undeclared (first use in this function) signing.c:301:8: note: each undeclared identifier is reported only once for each function it appears in signing.c:302:8: error: 'GPGME_PK_ECDH' undeclared (first use in this function) make[3]: *** [signing.lo] Error 1 make[3]: Leaving directory `/home/user/tmp/pacman/lib/libalpm' make[2]: *** [all-recursive] Error 1 make[2]: Leaving directory `/home/user/tmp/pacman/lib/libalpm' make[1]: *** [all-recursive] Error 1 make[1]: Leaving directory `/home/user/tmp/pacman' make: *** [all] Error 2