Auto merge of #27139 - pnkfelix:allow-disable-debuginfo, r=dotdash

fix `configure`: allow both `--enable-debug` and `--disable-debuginfo` in one invocation.

This is my very local fix to allow one to be able to (1.) build `rustc` and (2.) run `make check` with internal debug-mode *assertions* turned on in the presence of bugs like  #26447 and #26484 (both of which are solely caused by debuginfo and thus can be sidestepped via `--disable-debuginfo`).

This partially addresses #24416 (namely, it addresses the papercut outlined in the description of that ticket).  But there are other issues mentioned in the comment thread that are not addressed here, so they should be separately addressed before closing that ticket, or separate bugs should be opened for them.

configure

@@ -323,6 +323,17 @@ envopt() {
     fi
 }
 
+enable_if_not_disabled() {
+    local OP=$1
+    local UOP=$(echo $OP | tr '[:lower:]' '[:upper:]' | tr '\-' '\_')
+    local ENAB_V="CFG_ENABLE_$UOP"
+    local EXPLICITLY_DISABLED="CFG_DISABLE_${UOP}_PROVIDED"
+    eval VV=\$$EXPLICITLY_DISABLED
+    if [ -z "$VV" ]; then
+        eval $ENAB_V=1
+    fi
+}
+
 to_llvm_triple() {
     case $1 in
         i686-w64-mingw32) echo i686-pc-windows-gnu ;;
@@ -671,10 +682,12 @@ if [ -n "$CFG_ENABLE_DEBUG" ]; then
         CFG_DISABLE_OPTIMIZE=1
         CFG_DISABLE_OPTIMIZE_CXX=1
     fi
-    CFG_ENABLE_DEBUG_ASSERTIONS=1
-    CFG_ENABLE_DEBUG_JEMALLOC=1
-    CFG_ENABLE_DEBUGINFO=1
-    CFG_ENABLE_LLVM_ASSERTIONS=1
+
+    # Set following variables to 1 unless setting already provided
+    enable_if_not_disabled debug-assertions
+    enable_if_not_disabled debug-jemalloc
+    enable_if_not_disabled debuginfo
+    enable_if_not_disabled llvm-assertions
 fi
 
 # OK, now write the debugging options