Your command is a mix of single and multiple options. You will need to pass all parameters as separate list items instead of munging some into a long string and some alonw:

# "-o /usr/local/bin/dcraw -O4" needs to be a separated list:
    my @args= ("gcc","-o", "/usr/local/bin/dcraw","-O4","/Users/landry
+/Desktop/dcraw.c","-I/usr/local/include", "-L/usr/local/lib","-lm","-
+ljasper","-ljpeg", "-llcms2");
    system(@args) == 0
        or die "Couldn't launch [@args]: $? / $!";
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I assume that the current working directory is the same as when testing through the shell.