There are some usecases where we may want to append CFLAGS to the
default CFLAGS set by Git. This could for example be to enable or
disable specific compiler warnings or to change the optimization level
that code is compiled with. This cannot be done without overriding the
complete CFLAGS value though and thus requires the user to redeclare the
complete defaults used by Git.

Introduce a new variable `CFLAGS_APPEND` that gets appended to the
default value of `CFLAGS`. As compiler options are last-one-wins, this
fulfills both of the usecases mentioned above. It's also common practice
across many other projects to have such a variable.

While at it, also introduce a matching `LDFLAGS_APPEND` variable. While
there isn't really any need for this variable as there are no default
`LDFLAGS`, users may expect this variable to exist, as well.

Note that we have to use the `override` directive here such that the
flags get appended when compiling with `make CFLAGS=x CFLAGS_APPEND=y`.

Signed-off-by: Patrick Steinhardt <redacted>
---
 Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Makefile b/Makefile
index 2f5f16847a..b5252bed3d 100644
--- a/Makefile
+++ b/Makefile

@@ -1359,7 +1359,9 @@ endif
 # which'll override these defaults.
 # Older versions of GCC may require adding "-std=gnu99" at the end.
 CFLAGS = -g -O2 -Wall
+override CFLAGS += $(CFLAGS_APPEND)
 LDFLAGS =
+override LDFLAGS += $(LDFLAGS_APPEND)
 CC_LD_DYNPATH = -Wl,-rpath,
 BASIC_CFLAGS = -I.
 BASIC_LDFLAGS =

-- 
2.45.2.436.gcd77e87115.dirty