When compiling euler-1.60.6.tar.gz.
I've seen this while compiling several other programs as well.
I tried the CVS version of gcc as well as version 3.3.2.

Reading specs from /usr/gcc_cvs/lib/gcc/i686-pc-linux-gnu/3.5.0/specs
Configured with: ../gcc-cvs/gcc/configure --prefix=/usr/gcc_cvs
--x-includes=/usr/X11R6/include --x-libraries=w/usr/X11R6/lib
--enable-version-specific-runtime-libs --enable-threads
--with-cpu=athlon-mp --with-gnu-as --with-gnu-ld
Thread model: posix
gcc version 3.5.0 20040122 (experimental)

Reading specs from /usr/gcc332/lib/gcc-lib/i686-pc-linux-gnu/3.3.2/specs
Configured with: ../gcc-3.3.2/configure --prefix=/usr/gcc332
--enable-version-specific-runtime-libs --enable-threads
--with-cpu=athlon-mp
Thread model: posix
gcc version 3.3.2

gcc -Wall -O2 -DINSTALL_DIR=\"/usr\" -c metaps.c
metaps.c:211:29: missing terminating " character
metaps.c:213: error: `y2' undeclared here (not in a function)
metaps.c:213: error: parse error before "exch"
metaps.c:213: error: stray '\' in program
metaps.c:213: error: stray '\' in program
metaps.c:213: error: stray '\' in program
metaps.c:213: error: stray '\' in program
metaps.c:213: error: stray '\' in program
metaps.c:213: error: stray '\' in program
metaps.c:218:8: missing terminating " character
metaps.c: In function `ps_meta_line':

gcc -v -save-temps -Wall -O2 -DINSTALL_DIR=\"\" -c metaps.c
Reading specs from /usr/gcc332/lib/gcc-lib/i686-pc-linux-gnu/3.3.2/specs
Configured with: ../gcc-3.3.2/configure --prefix=/usr/gcc332
--enable-version-specific-runtime-libs --enable-threads
--with-cpu=athlon-mp
Thread model: posix
gcc version 3.3.2
 /usr/gcc332/lib/gcc-lib/i686-pc-linux-gnu/3.3.2/cc1 -E -quiet -v
-D__GNUC__=3 -D__GNUC_MINOR__=3 -D__GNUC_PATCHLEVEL__=2 -DINSTALL_DIR=""
metaps.c -Wall -O2 metaps.iignoring nonexistent directory
"/usr/gcc332/i686-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/gcc332/include
 /usr/gcc332/lib/gcc-lib/i686-pc-linux-gnu/3.3.2/include
 /usr/include
End of search list.
metaps.c:211:29: missing terminating " character
metaps.c:218:8: missing terminating " character
make: *** [metaps.o] Error 1


Fred