configure fails with message: 
[...] 
checking for PCRE support... yes 
checking for memmove... (cached) yes 
checking for PDFlib support... yes 
checking for the location of libtiff... yes 
checking for jpeg_read_header in -ljpeg... no 
configure: error: libjpeg not found! 
 
!!! ERROR: dev-php/mod_php-4.3.1 failed. 
!!! Function src_compile, Line 217, Exitcode 1 
!!! bad ./configure 
 
I tracked this down to a 
-L/opt/sun-jdk-1.4.1.01/jre/lib/i386 linker option which 
puts /opt/sun-jdk-1.4.1.01/jre/lib/i386/libjpeg.so before 
/usr/lib/libjpeg.so in the library search path. The 
sun-jdk libjpeg.so does however not fulfill the 
requirements of mod_php as /usr/lib/libjpeg.so from the 
libjpeg-6b package would. 
 
The configure line used by Gentoo Linux is the following: 
 
./configure --prefix=/usr --with-bz2 --enable-ftp 
--enable-force-cgi-redirect --enable-discard-path 
--enable-mime-magic --enable-wddx --enable-dbase 
--with-zlib=yes --with-iconv --enable-bcmath 
--enable-sysvsem --enable-exif --enable-sysvshm 
--enable-sockets --enable-calendar --enable-trans-sid 
--enable-safe-mode --enable-versioning --enable-track-vars 
--enable-inline-optimization 
--with-config-file-path=/etc/php4 --host=i686-pc-linux-gnu 
--without-readline --with-pam --with-gettext 
--with-openssl --with-gdbm=/usr --with-db3=/usr 
--with-mysql=/usr --with-ttf --with-t1lib 
--with-pdflib=/usr --with-jpeg-dir=/usr --with-pspell 
--with-png-dir=/usr/lib --with-zlib 
--with-zlib-dir=/usr/lib --with-exec-dir=/usr/bin 
--with-apxs=/usr/sbin/apxs --with-qtdom --with-xml 
--with-dom --with-mcrypt --with-mhash 
--disable-posix-threads --with-java=/opt/sun-jdk-1.4.1.01 
--with-xpm-dir=/usr/X11R6 
 
I was about to file a Gentoo Linux bug (at 
bugs.gentoo.org), but figured this failure might happen in 
other environments, too. 
 
My guessed fix proposal is to separate the java and 
libjpeg linker options in configure.in as well as in the 
extension modules' Makefiles to prevent this clashing.