Building Xorg server 7.4 resulted in the following, openssl/sha.h not found during the build.  I would thus think that the configure script should include a check for availability of the openssl dev kit, which would appear to be a dependency.

gcc -DHAVE_CONFIG_H -I. -I../include -DHAVE_DIX_CONFIG_H -Wall -Wpointer-arith -Wstrict-prototypes -Wmissing-prototypes -Wmissing-declarations -Wnested-externs -fno-strict-aliasing -D_BSD_SOURCE -DHAS_FCHOWN -DHAS_STICKY_DIR_BIT -I/usr/include/freetype2 -I/usr/include/pixman-1 -I../include -I../include -I../Xext -I../composite -I../damageext -I../xfixes -I../Xi -I../mi -I../miext/shadow -I../miext/damage -I../render -I../randr -I../fb -g -O2 -MT glyph.lo -MD -MP -MF .deps/glyph.Tpo -c glyph.c  -fPIC -DPIC -o .libs/glyph.o
glyph.c:30:25: error: openssl/sha.h: No such file or directory
glyph.c: In function 'HashGlyph':
glyph.c:205: error: 'SHA_CTX' undeclared (first use in this function)
glyph.c:205: error: (Each undeclared identifier is reported only once
glyph.c:205: error: for each function it appears in.)
glyph.c:205: error: expected ';' before 'ctx'
glyph.c:208: warning: implicit declaration of function 'SHA1_Init'
glyph.c:208: warning: nested extern declaration of 'SHA1_Init'
glyph.c:208: error: 'ctx' undeclared (first use in this function)
glyph.c:212: warning: implicit declaration of function 'SHA1_Update'
glyph.c:212: warning: nested extern declaration of 'SHA1_Update'
glyph.c:220: warning: implicit declaration of function 'SHA1_Final'
glyph.c:220: warning: nested extern declaration of 'SHA1_Final'
make[1]: *** [glyph.lo] Error 1
make[1]: Leaving directory `/big/Downloads/xorg-server-1.5.1/render'
make: *** [all-recursive] Error 1