Jetzt will ich jedoch MySQL-Unterstützung zu meinem Modul hinzufügen, wofür ich aber den Pfad "/usr/include/mysql" mit includen müsste.

Wenn ich eine normale Konsolen-Anwendung (also kein Apache Modul) mit MySQL-Unterstützung kompilieren würde, würde ich das so machen:

gcc -c -I/usr/include/mysql mysql.c
gcc -o mysql mysql.o -L/usr/lib/mysql -lmysqlclient

Allerdings sieht meine Makefile jetzt so aus, und ich weiß nicht wo ich dort die Includes einbauen muss:

##
##  Makefile -- Build procedure for mod_layerad Apache module
##
builddir=$(shell pwd)
top_srcdir=/usr/share/apache2
#usr/local/apache2
top_builddir=/usr/share/apache2
#usr/local/apache2
include /usr/share/apache2/build/special.mk
#usr/local/apache2/build/special.mk

#   the used tools
APXS=/usr/bin/apxs2
APACHECTL=apache2ctl
CC=`$(APXS) -q CC`
INC=-I`$(APXS) -q INCLUDEDIR` `$(APXS) -q CFLAGS`  #-DLAYOUT_FILEOWNER_NAME
LD_SHLIB=`apxs -q LDFLAGS_SHLIB`
VERSION = 1.0.0
DISTNAME = mod_layerad
DISTVNAME = $(DISTNAME)-$(VERSION)

SRC = mod_layerad.c
OBJ = ${SRC:.c=.o}
SOBJ = ${SRC:.c=.lo}

SHELL = /bin/sh
PERL = perl
NOOP = $(SHELL) -c true
RM_RF = rm -rf
SUFFIX = .gz
COMPRESS = gzip --best
TAR  = tar
TARFLAGS = cvf
PREOP = @$(NOOP)
POSTOP = @$(NOOP)
TO_UNIX = @$(NOOP)

#   additional defines, includes and libraries
# Apache itself won't compile with it this strict
#DEF = -Wall -DDEBUG -Wtraditional -Wshadow -Wid-clash-len -Wpointer-arith -Wcast-qual -Wcast-align -Wwrite-strings-Wconversion -Waggregate-return -Wstrict-prototypes -Wmissing-prototypes -Wmissing-declarations -Wredundant-decls -Wlong-long -Winline -Werror
#DEF = -Wall -DDEBUG 

#   the default target
all: mod_layerad.so

#   compile the shared object file
#mod_layout.so: $(OBJ)  Makefile
mod_layerad.so: $(OBJ)
	$(APXS) -o liblayerad.la -c $(SOBJ)
	#$(APXS) -c -o liblayerad $(SOBJ)
	#$(APXS) -i -a mod_layerad.la

mod_layerad.o : mod_layerad.c
	$(APXS) -c mod_layerad.c

#   install the shared object file into Apache 
install: 
	$(APXS) -i -n liblayerad.so -e liblayerad.la
	@echo "+--------------------------------------------------------+"; \
	echo "| All done.                                              |"; \
	echo "|                                                        |"; \
	echo "| You will need to add the directive:                    |"; \
	echo "| LoadModule layerad_module modules/liblayerad.so        |"; \
	echo "|                                                        |"; \
	echo "| So that you can begin to use mod_layerad.              |"; \
	echo "|                                                        |"; \
	echo "| Thanks for installing mod_layerad.                     |"; \
	echo "+--------------------------------------------------------+"; \

#   cleanup
clean:
	rm -f mod_layerad.o mod_layerad.so $(OBJ) *.gz *rpm

Bin für jede Hilfe dankbar.
Jonas