build: move -std=gnu11 to CFLAGS

It doesn't logically belong in CDEBUGFLAGS.

Makefile now *prepends* its default CPPFLAGS and CFLAGS to the environment-
supplied flags. This allows the user to override individual flags by setting
these variables through configure, without disturbing all the rest of the
flags that Makefile wants by default.

Changelog-None

Author: whitslack

Makefile

@@ -289,8 +289,9 @@ PKG_CONFIG_PATH := $(SQLITE_PREFIX)/lib/pkgconfig:$(PKG_CONFIG_PATH)
 endif
 endif
 
-CPPFLAGS += -DCLN_NEXT_VERSION="\"$(CLN_NEXT_VERSION)\"" -DPKGLIBEXECDIR="\"$(pkglibexecdir)\"" -DBINDIR="\"$(bindir)\"" -DPLUGINDIR="\"$(plugindir)\"" -DCCAN_TAL_NEVER_RETURN_NULL=1 -DSHACHAIN_BITS=48 -DJSMN_PARENT_LINKS
-CFLAGS = $(CWARNFLAGS) $(CDEBUGFLAGS) $(COPTFLAGS) -I $(CCANDIR) $(EXTERNAL_INCLUDE_FLAGS) -I . -I$(CPATH) $(SQLITE3_CFLAGS) $(SODIUM_CFLAGS) $(POSTGRES_INCLUDE) $(FEATURES) $(COVFLAGS) $(DEV_CFLAGS) $(PIE_CFLAGS) $(COMPAT_CFLAGS) $(CSANFLAGS)
+# Put the environment-inherited flags *last* so the user has the final say.
+CPPFLAGS := -DCLN_NEXT_VERSION="\"$(CLN_NEXT_VERSION)\"" -DPKGLIBEXECDIR="\"$(pkglibexecdir)\"" -DBINDIR="\"$(bindir)\"" -DPLUGINDIR="\"$(plugindir)\"" -DCCAN_TAL_NEVER_RETURN_NULL=1 -DSHACHAIN_BITS=48 -DJSMN_PARENT_LINKS $(CPPFLAGS)
+CFLAGS := $(CWARNFLAGS) $(CDEBUGFLAGS) $(COPTFLAGS) -I $(CCANDIR) $(EXTERNAL_INCLUDE_FLAGS) -I . -I$(CPATH) $(SQLITE3_CFLAGS) $(SODIUM_CFLAGS) $(POSTGRES_INCLUDE) $(FEATURES) $(COVFLAGS) $(DEV_CFLAGS) $(PIE_CFLAGS) $(COMPAT_CFLAGS) $(CSANFLAGS) $(CFLAGS)
 
 # If CFLAGS is already set in the environment of make (to whatever value, it
 # does not matter) then it would export it to subprocesses with the above value

configure

@@ -166,10 +166,14 @@ set_defaults()
     # which matters since you might explicitly set of these blank.
     PREFIX=${PREFIX:-/usr/local}
     CC=${CC:-cc}
+    # A more compact way of setting the default value of a variable.
+    # Similar to the above, ":=" means assign if empty or unset; "=" means assign only if unset.
+    # The quotes suppress the globbing that would otherwise occur after variable expansion.
+    : "${CFLAGS=-std=gnu11}"
             # Detect macOS and use appropriate debug flags for libbacktrace compatibility
     if [ "$(uname -s)" = "Darwin" ]; then
         # Always override to avoid DWARF 5
-        CDEBUGFLAGS="-std=gnu11 -g -gdwarf-4 -fno-standalone-debug -fstack-protector-strong"
+        CDEBUGFLAGS="-g -gdwarf-4 -fno-standalone-debug -fstack-protector-strong"
         # Set SDKROOT for macOS
         SDKROOT="$(xcrun --sdk macosx --show-sdk-path)"
 
@@ -178,7 +182,7 @@ set_defaults()
             echo "Warning: dsymutil not found. Install Xcode Command Line Tools for better debug support."
         fi
     else
-        CDEBUGFLAGS=${CDEBUGFLAGS--std=gnu11 -g -fstack-protector-strong}
+        CDEBUGFLAGS=${CDEBUGFLAGS--g -fstack-protector-strong}
     fi
     DEBUGBUILD=${DEBUGBUILD:-0}
     COMPAT=${COMPAT:-1}
@@ -233,6 +237,7 @@ usage()
     # We assume we have a modern gcc.
     DEFAULT_CWARNFLAGS="$(default_cwarnflags ""$DEFAULT_COPTFLAGS"" 1 1)"
     usage_with_default "CC" "$CC"
+    usage_with_default "CFLAGS" "$CFLAGS"
     usage_with_default "CWARNFLAGS" "$DEFAULT_CWARNFLAGS"
     usage_with_default "COPTFLAGS" "$DEFAULT_COPTFLAGS"
     usage_with_default "CDEBUGFLAGS" "$CDEBUGFLAGS"
@@ -607,6 +612,7 @@ fi
 add_var PREFIX "$PREFIX"
 add_var CC "$CC"
 add_var CONFIGURATOR_CC "$CONFIGURATOR_CC"
+add_var CFLAGS "$CFLAGS"
 add_var CWARNFLAGS "$CWARNFLAGS"
 add_var CDEBUGFLAGS "$CDEBUGFLAGS"
 add_var COPTFLAGS "$COPTFLAGS"