[3.12] gh-117752: Autoconf: store all LLVM profile data in the build directory (GH-117790) (#117795)

This prevents spurious 'env changed' and llvm-profdata merge errors.

(cherry picked from commit 396b831)

Co-authored-by: Erlend E. Aasland <[email protected]>

Author: miss-islington

configure

@@ -1989,7 +1989,7 @@ case $CC in
     PGO_PROF_GEN_FLAG="-fprofile-instr-generate"
     PGO_PROF_USE_FLAG="-fprofile-instr-use=code.profclangd"
     LLVM_PROF_MERGER="${LLVM_PROFDATA} merge -output=code.profclangd *.profclangr"
-    LLVM_PROF_FILE="LLVM_PROFILE_FILE=\"code-%p.profclangr\""
+    LLVM_PROF_FILE="LLVM_PROFILE_FILE=\"\$(shell pwd)/code-%p.profclangr\""
     if test $LLVM_PROF_FOUND = not-found
     then
       LLVM_PROF_ERR=yes
@@ -2005,7 +2005,7 @@ case $CC in
         PGO_PROF_GEN_FLAG="-fprofile-instr-generate"
         PGO_PROF_USE_FLAG="-fprofile-instr-use=code.profclangd"
         LLVM_PROF_MERGER="${LLVM_PROFDATA} merge -output=code.profclangd *.profclangr"
-        LLVM_PROF_FILE="LLVM_PROFILE_FILE=\"code-%p.profclangr\""
+        LLVM_PROF_FILE="LLVM_PROFILE_FILE=\"\$(shell pwd)/code-%p.profclangr\""
         if test "${LLVM_PROF_FOUND}" = "not-found"
         then
           LLVM_PROF_ERR=yes