distcc-avahi: fix FORTIFY buffer overflow in dcc_gcc_rewrite_fqn

pkgrel 16 builds ship an upstream distcc 3.4 bug: src/compile.c sizes
the rewritten-compiler-name buffer with strlen(argv[0] + 1) — pointer
arithmetic applied before strlen — under-allocating by 2 bytes. glibc
FORTIFY_SOURCE=2 catches the resulting overflow in strcat and aborts,
so every "distcc gcc ..." invocation dies on a modern Arch.

Patch moves the +1 outside the strlen, as intended.
Closes marfrit/marfrit-packages#3.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

arch/distcc-avahi/fix-gcc-rewrite-fqn-overflow.patch

@@ -0,0 +1,21 @@
+Description: fix off-by-paren in dcc_gcc_rewrite_fqn buffer sizing
+ src/compile.c's dcc_gcc_rewrite_fqn() allocates a buffer for
+ "<target>-<argv[0]>\0" but writes strlen(argv[0] + 1) — pointer
+ arithmetic *then* strlen, which under-allocates by 2 bytes and trips
+ glibc FORTIFY_SOURCE=2 with "*** buffer overflow detected ***"
+ on any `distcc gcc …` invocation.
+ Intent was strlen(argv[0]) + 1 (length plus terminator).
+Bug-reauktion: marfrit/marfrit-packages#3
+Author: Markus Fritsche <mfritsche@reauktion.de>
+
+--- a/src/compile.c
++++ b/src/compile.c
+@@ -579,7 +579,7 @@ static int dcc_gcc_rewrite_fqn(char **argv)
+         return -ENOENT;
+
+
+-    newcmd_len = strlen(target_with_vendor) + 1 + strlen(argv[0] + 1);
++    newcmd_len = strlen(target_with_vendor) + 1 + strlen(argv[0]) + 1;
+     newcmd = malloc(newcmd_len);
+     if (!newcmd)
+         return -ENOMEM;